One of the things that is supposed to be coming with iOS 8 is the ability to AirPlay directly to an Apple TV, without a shared network. If it happens, and it looks like it should, then all you need is an Apple TV and the appropriate cable to make any projector ad-hoc capable with your iPad.
Heck, with a good selection of cables, you could skip carrying the projector and just borrow whatever is available at your destination.
Until then, you still need a shared network (or connect directly to the projector from the iPad). Though you could carry your own router and set it up as a private network, just for your iPad, Apple TV, and projector.