I want to stay away from keyboard controls as much as possible. The whole game is designed around being able to play it with just the mouse and a drink in the other hand :-) Also it's designed to not require quick using of items. When you're in a situation where you want to use something always just click the left mouse button. Wherever you do this, this will pause the game. You can now in your own time pick the item you want to use and click that. Some items (e.g. the booster) don't automatically resume the game after you activate them giving you a chance to put your mouse back where you want it and then resume the game. I a way my idea is to let that part feel more like a turn based game. All ship weapons work like this too (they're not twitch/reflex based) once you for example have a beam weapon: You first pause the game by left clicking then click the beam-item you want to use (or immediately click the beam-weapon item which will also pause the game), then you will see a firing arc and those things you can pick as targets you will be able to pick at your own leisure. Once you pick a target the beam fires and the game automatically resumes. Most thing work like this. Some weapons have annoying small firing arcs so they do require a bit of timing when to pause to line them up but this is intentional; these usually have better versions with better firing arcs.
Here's a link to the part in the 2nd tutorial where you might be able to follow what I mean (I remember you're hard of hearing right?) but just seeing it might illustrate what I'm trying to explain better: