A simple bottle dynamo is the best option.
No batteries to rely on, and light available whenever you need it.
No hub dynamo that constantly steals energy even when it's not used (not much, but more than people seem to think).
The higher efficiency of a hub dynamo isn't that great anyway.
Weight is negligible. We're talking less than a pound for the entire installation - dynamo, cables and lamp.
The rear light should be a battery-powered LED. They last long enough not to require more than maybe one change of batteries during a tour, depending on how long you plan to tour for.