I thought of some problems people have with armors. If you are about to wear nano or quantum-armor you normally only wear 3 pieces since the chest-piece is reserved for bat or lappack. With non-electric weapons the Nano/Q-Chestpieces will have a purely military usage. But still some other Chestpieces could fit as alternative improvements to the batpack (next to the lappack which is the only improvement of the batpack actually).
1. Small Change in the Electric-Jetpack
Maybe just switch the Batbox with a Batpack and allow the electric jetpack to work like a normal batpack in addition to flying.
2. Backpack-Addition
It's a Batpack with some additional space to store some items (maybe 9 slots?), I don't really know if it is possible to create an additional inventory if you use a certain item. But again IC2 does some things that I not believed to be possible earlier :P, maybe it could be used to store ammunition later.
3. Hazmat-Addition
I read about the Hazmat-Suit. In most cases you will be wearing it while mining to avoid lava-damage or falling-damage. Then again a chestpiece which can't store energy makes it unlikely that people even use it.
I would price the Backpack similar to the Lappack since it is quite useful. The E-Jetpack is expensive enough. And the Hazmat-Suit will have the drawpack of losing energy upon damage (since it protects against quite a lot of things, and if it would not break or deplete it would be too strong.