I like the idea of Coke And Mentos bombs. Probably should do no damage, or very slight damage.
PDA bomb should NEVER gib. Maybe knock to critical or come very close on an unarmored target standing on it.
How about a:
Radio Signalling Device + High Capacity cell + PDA + Wires (screwdriver, multitool, and wirecutters needed)
First, screwdriver the PDA, then add Wires, wirecut, add Cell, add Signaller, screwdriver, then multitool.
Activating the PDA's flashlight now sets off a timer (set during the Multitool step), that when it runs out, sends a signal over whatever frequency it was set to, and shorts it out/stops it from working as well as emits a deafening noise. It should probably only temporarily disable PDAs, and affect nothing else. Does no damage.
Soda Can + Grenade Casing + Timer: "Fake Grenade"
It looks like a real grenade, but it isn't! Fool your friends into thinking you're a traitorous swine! Counts down. Forever.
Possibly a Chem reaction to give us metal-foam esque Silly String? Much weaker, of course.
High Capacity Cell + Wires + Flashlight (using) Screwdriver:
Bootleg flasher. Does not function as a flashlight. It has a chance to break, causing it to be utterly useless.
Oxygen Tank + Rod + Blowtorch + Metal
Different kind of bootleg rifle. Basically a t-shirt cannon, but it fires metal rounds. More accurate, but only knocks down at close range and does little damage. It's also large (2 hands.)
Hatchet + Igniter + Power Cell
Activating the hatchet and throwing it treats it like a projectile. Has a chance to do high damage, but is somewhat inaccurate, has about an 80% chance to do very little damage, and is basically a rocket propelled hatchet.
Stunprod + Metal + Igniter + Plasma Tank
The king of improvised firearms. Knocks down, does some damage (takes 5-7 on unarmored targets), and is pretty accurate. Requires plasma to fire, but dosen't actually use it up (like the flamethrower, except it dosen't use the plasma)