All you need is a box with straps (for a back pack), some vacuum cleaner hose, pump action water gun (attached to the vacuum hose) and some grey overalls and boots.
last dressup i had i purchased a Gumby costume.. good fun lol.. even though it originally started in the late 50s n early 60s, it was revived in the 80s so thats an option.
other options
Rambo, Predator, Tony Montana (scarface), Slash (GNR)