Thanks for the ideas once again, Panther!
There are going to be two types of upgrades you can buy-- jet items, and augmentations. Augmentations are passive, and are always effecting your player. Jet Items are things that you specifically call upon by pressing the jet key.
The current augments I have are speed, size, damage, jump height, and wall climbing.
As I type this I've only made one jet item, a force field. Anyone caught it in when it is triggered gets flung upwards.
Edit: Another, more expensive one that I made is where you can possess other players for a short amount of time. The con is that your body is left vulnerable while doing this.