How big are your sectionals? Brass or woodwinds?
Anything from Anker will be solid and relatively inexpensive. JBL is also very good, but more expensive (might last longer). If you're dealing with a few clarinets, the pocket-sized ones (10-20 watts) will be fine. For a handful of trumpets, something more like 30-50 watts. Bigger than that, shoot for 80-100. This will fit in a backpack, but you won't have room for much else.