Three which haven't been tried yet, along with why they probably won't work.
Air travel Not realistic. With a lot of work, they might be able to assemble and coat enough fabric for a very small balloon, but they have no helium and rigging a hot-air burner isn't exactly casual work. Hang gliders might be easier if you know what you're doing in the construction, but the buildings aren't that tall and gliding doesn't give you much range at low heights. Still, up and out has to be on someone's mind -- we don't know if the microwave barrier is a wall or a dome. But any air travel they could conceivably put together would be slow -- and very easy to stop.
Microwave shielding I'm surprised Graham hasn't tried this. There's plenty of stuff out there which stops microwaves, some of which might be found in a decently-stocked kitchen. Wrap someone up head-to-toe, and they just might be able to blunder through the barrier. The issue here is that while it's possible, it might just bring them up against the next defense.
Sewers Too classic not to have been stopped during the initial design stage. The town is probably running on a small sealed water recirculation supply with very tiny pipes.