Travel guides: It might not be cheaper, but books are heavy. Buy locally when you need them, it also provides some money to people much poorer than you without giving them a hand out.

Room and board: Stay in hostels where possible, they meet a lot of interesting people.

Transportation: Take ground transport where possible, you see a lot more and meet a lot of interesting people on those long journeys.

Packing: depends where you are going. Hot countries you can get away with a side bag, cold countries you need more.