Fender still makes a small battery powered amp which will accept a mic input as well as a guitar (or other) input. It's called The Amp Can. It is quite durable, includes a charger and weighs (I'm told) about 13 lbs. I've several times tried one in the shops but haven't yet bought one. 15 watts isn't much, but it's enough to give some presence to an outdoor performance, and might be exactly what you need. Good luck.

Peace, Mooh.