If you need to buy gear, get it from the classifieds, craigslist, ebay, buy it used, or borrow it from friends.
Stay in hostels, rather than hotels. Stay in a tent, rather than a hostel.
Take a train instead of a plane. Walk or get the bus instead of taking a taxi. Hitchhike instead of taking a train or bus.
Don’t buy water, use a plastic bottle filled and topped up with tap water.
Don’t eat out in restaurants every day, especially in Europe. Supermarkets and bakeries are so much cheaper and the food is often better (than McDonalds, for sure).
You can cook for yourself in hostels, and, if camping, you can use a stove to make some great meals.
