I posted a link to $120 K2 energy lithium iron battery. Its included in the final prices I posted too. Third option, first link.
You put the battery in a case, put the inverter and the charger in separate compartments of that case, or another case.
If you're only planning on playing for 2.5 hours, leave the charger at home.
The charger I posted runs at a 10 amp charge rate. Will charge the K2 energy (a professional lithium iron with a solid BMS system in it and it's brand new) battery in 1.2 hours. Play for 2 hours, charge for 1, play again for 2.
Charge at the Starbucks. Never short it though, not even for a millisecond.
Looks a little like this. My battery is 4x the size of the K2 battery I posted for you. My inverter is about 3x bigger than the one I posted for you as well:
