Glad you're enjoying it! Nothing for now on donations, unfortunately, I didn't expect many people to pick it up.
I'll have to admit that the backpacks don't do anything yet other than take up weight. I'm planning on having them give both a passive buff and an active skill (usable from a face button or a key) but I haven't quite gotten them to work right, especially for garage calculations.
The rotary gun and focus laser both increase in potency (rate of fire for rotary gun, damage and range for focus laser) the longer they're held down. On the other hand, the drain while firing increases proportionately, slowing down your energy regeneration further. You can look at the output bar (the smaller blue bar to the right of the radar) and see the red segment increase as you hold it down.