While running a d20 Modern campaign at the home of my friends, Joe and Sarah, I needed something to represent a fishing boat that the bad guys were using to launch Stinger missiles at the heroes' aircraft. We ended up using their 4-year old daughter's Sesame Street toy boat. There's something disturbing about seeing rocket-toting demons standing next to Bert & Ernie. :)
Elsewhere in that campaign, we used a three-inch tall plastic Snoopy to represent a Large monster ... an urban wendigo, IIRC. "Giant Snoopy shall pick the flesh from your bones!"