Since I have started to be more nano-focused in my newer eve career, I came across a Backpack quite quickly and decided I would need one as well. Essentially a Backpack is a ship that anchors on your main and provides you with links. The ship most often used for this role is the Bifrost, because it is fast and provides a bonus for skirmish command bursts. But what exactly should you put on it?
I think proper theorycrafting should always start with writing down what you want to achieve, so let’s write down the requirements (in descending order of importance):
- Needs to keep up with my main
- Needs to provide Links
- Should not die before my main does
- Should be able to reposition my main
- Might need to hold tackle (point or scram)
- Might need to boosh enemies
- Might need to provide charges/reps out of combat
- Might Scan a new Chain
Building the Fits
Let’s start with the most important requirements.  is simple, put a 5mn MWD on there is a little bit more complicated. On Backpacks typically Skirmish and sometimes also Shield Links are used. From the 3 Skirmish Links, 2 are pretty much mandatory.
- Rapid Deployment Charges, increasing raw Speed
- Interdiction Maneuvers Charges, increasing the Range of Points and defensive Webs/Scrams
So I am definitely running those 2 and might run a third one as either skirmish or shield (and maybe even armor if needed, but I don’t know if a Magus would be better for that)
Moving on to the other highslots, we can tick  and  . with an offline probe launcher, an Small Remote Armor Repairer and a Small Remote Hull Repairer. I often see people leaving these slots completely empty but since these modules cost less than 1m ISK combined, one might as well put them in all the fits and who knows when they will be handy.
Now we are left with [3-6]. This is where things are getting interesting
For the remaining 4 midslots there is a whole bunch of stuff that could be useful, and which requirements are benefiting from them.
- Micro Jump Field Generator [4, 6]
- Point, keeping a 2nd guy from warping 
- Scram, allowing you to selectively boosh, or scram of someone burning after you [3, 5, 6]
- small cap booster, allowing you to hold neuting targets 
- 1mn Afterburner [3, 6]
- Medium Shield Extender 
This is very interesting, as certain modules do a lot more things than others, and the grouping of 4 out of 6 modules determines the capability of the fit. I came up with 3 combinations that seem to make sense together in the end, but I am pretty sure there is a lot more interesting things possible.
The first one is meant to cover the part of a repositioning Tool, and might be able to also boosh unsuspecting enemies who don’t warp away immediately. To maximize the number of options with the MJFG it comes with a Scram, and because people might scram back it also comes with an afterburner. Since I run XLASB’s most of the time I put cap charges in the cargohold. You can’t really make this work with a DCU so the lows ended up all speed mods, 2x Nano 1x Overdrive is the most efficient combination for distance over time. If you go with a more expensive CN scram then you can even make the DCU work. To be honest this one could do a lot more when you actively pilot it instead of just sitting as a Backpack, and will also be the one that I use to try to rescue others.
Dual Prop (6mn) Scram Bifrost
[Bifrost, 6mn] Nanofiber Internal Structure II Nanofiber Internal Structure II Overdrive Injector System II 5MN Quad LiF Restrained Microwarpdrive Republic Fleet Medium Shield Extender Warp Scrambler II Micro Jump Field Generator 1MN Afterburner II Core Probe Launcher I /OFFLINE Small Remote Hull Repairer I /OFFLINE Small I-ax Enduring Remote Armor Repairer /OFFLINE Skirmish Command Burst II, Evasive Maneuvers Charge Skirmish Command Burst II, Interdiction Maneuvers Charge Skirmish Command Burst II, Rapid Deployment Charge Small Command Processor I Small Command Processor I Navy Cap Booster 400 x18 Nanite Repair Paste x50 Core Scanner Probe I x16 Evasive Maneuvers Charge x300 Interdiction Maneuvers Charge x300 Rapid Deployment Charge x300 Agency 'Overclocker' SB3 Dose I x2
This is the fit that I ended up using the most. The CN Scram doesn’t really make sense as you die quite quickly, but a Damage Control would definitely be very handy to add. I have thought about replacing the Overdrive with a Compact DCU and getting a CN MSE and scoped Scram a few times, this ends up being exactly AP’s fit.
Next is the more defensive one. The reason I decided to go for a cap booster is that I fly in w-space mostly, and there is just bound to be a Megathron with 7 heavy neuts one day, it’s just a matter of time. Other than that it is pretty straightforward. Your cap booster cycles faster than a single Heavy Neut, so that should be covered. If you don’t need your charges for an XLASB ship then switching to Navy Cap Booster 100’s might be an option. That way you get four injects from dry cap before you have to reload, and mostly can keep point even under 2 staggered Heavy Neuts as well.
5mn Point Injector Bifrost
[Bifrost, 5mn] Nanofiber Internal Structure II Nanofiber Internal Structure II Overdrive Injector System II 5MN Quad LiF Restrained Microwarpdrive Republic Fleet Medium Shield Extender Small F-RX Compact Capacitor Booster, Navy Cap Booster 400 Micro Jump Field Generator Warp Disruptor II Core Probe Launcher I /OFFLINE Small Remote Hull Repairer I /OFFLINE Small I-ax Enduring Remote Armor Repairer /OFFLINE Skirmish Command Burst II, Evasive Maneuvers Charge Skirmish Command Burst II, Rapid Deployment Charge Skirmish Command Burst II, Interdiction Maneuvers Charge Small Command Processor I Small Command Processor I Navy Cap Booster 400 x24 Nanite Repair Paste x50 Core Scanner Probe I x16 Evasive Maneuvers Charge x300 Interdiction Maneuvers Charge x300 Rapid Deployment Charge x300 Agency 'Overclocker' SB3 Dose I x2
This last one is a little different, it only has a 10mn afterburner, making it Ideal to boosh unwilling targets and keeping them tackled while doing so. I initially had a Point and Scram on this one, as I felt like it would be great to keep a roller tackled all the way through the boosh. Later I switched to Scram and Injector, as people don’t use those 5-6 seconds to their advantage usually, and only try to scram you (which doesn’t work without a Sensor Booster). The problem is of course that it handles like a freight train. Interestingly if you sit on a Hole at 0 at align, heat your ab, and boosh immediately then usually you end up just in the right position to get rollers. Combined with the really small sig this is a really potent way to get rollers of the hole. With this newly defined role I finally also put a cloak on there. Useful for sitting at holes, but also more useful for cloaking and booshing on the exactly same tick (doesn’t work otherwise, but knocks of another 1-2 ticks of the time that someone can lock and scram you, increasing your chance of getting a boosh of successfully even more).
[Bifrost, 2link 10mn MSE Inject] Nanofiber Internal Structure II Navy Micro Auxiliary Power Core Damage Control II 10MN Y-S8 Compact Afterburner Republic Fleet Medium Shield Extender Small F-RX Compact Capacitor Booster, Navy Cap Booster 25 Faint Epsilon Scoped Warp Scrambler Micro Jump Field Generator Core Probe Launcher I Small I-ax Enduring Remote Armor Repairer Small Remote Hull Repairer I Skirmish Command Burst II, Evasive Maneuvers Charge Skirmish Command Burst II, Rapid Deployment Charge Prototype Cloaking Device I Small Command Processor I Small Core Defense Field Extender II Navy Cap Booster 400 x32 Nanite Repair Paste x50 Core Scanner Probe I x16 Agency 'Overclocker' SB3 Dose I x2
So that’s what I came up with pretty much. I did of course also consult with my corp mates and did an extensive search through Zkillboard, and all fits that I found have been some kind of variation of these similar concepts. I think there are only a few people that run cap boosters, most people seem to prefer some more tank. The dual prop version however has been gaining popularity recently, spearheaded by Auraus Porcaleus and his impressive flying, with the Tuskers in pursuit. And according to my corp mate Web Driver (don’t worry, I will write your name correctly), some people swear by 10mn Bifrosts. I haven’t found them on Zkillboard yet, but who knows maybe they are out there as Backpacks too?
If you now want something completely different than just backpacks, here are two other ways to fly the Bifrost, I won’t tell you what they are good for tho if they are good for anything at all.