there are battery-powered amplifiers and small PA systems available on the market. the PA system will give you the most hi-fi sound, most guitar amps are not voiced for classical guitar. for about $70 you can purchase a Kremona pickup with installs on top of the bridge, held on by the strings, and it works quite well in that setting (outdoors with noise), doesn't pick up wind noise, and needs no alteration of the guitar. the Bose S1 is excellent: a charge lasts 6-8 hours, the sound is great, and it's small and portable, with 2 channels if you also sing. Crate made 3 different battery amps; the Taxi, mentioned above, the Limo, slightly larger with effects, and the Bass Buss; the Limo is really nice, but hard to find.
Lester Devoe Flamenco Negra
Lester Devoe Flamenco Blanca
Aparicio Flamenco Blanca with RMC pickup
Bartolex 7-string with RMC pickup
Giannini 7-string with Shadow pickup
Sal Pace 7-string archtop