Busses, not planes.
In South America, at least, busses were way cheaper than planes. And, even though busses take longer, they are way more comfortable! You can also get overnight busses, so basically you're paying for a hostel on wheels while getting you where you need to go.
Do you really need that?
Go easy on the souvenirs. You don't have a lot of room in your pack. Before buying something, think if you will actually need and appreciate it once you get home.
Eat at the local resturants.
Typically, the touristy restaurants are more expensive. But really, are you seriously going to travel to a different country and eat at a tourist restaurant? No. The local food in Perú was amazing, with a two course meal for $2 USD. To really immerse yourself into a different culture, you should to eat like a local.
Find the cheapest hostels.
Find the cheapest hostels with the accommodations you are looking for. This is really easy to do if you have the HostelWorld app. We barely spent any money at the hostels by choosing the cheapest ones, but all the ones we stayed at were pretty nice.
Don't travel luxuriously.
Honestly, you shouldn't find a lot of traveling luxurious unless your 65, retired, and on a cruise ship. You can live comfortably once you get back home. Part of traveling is going without the basic luxuries you have in your normal life; it puts it all into perspective, allowing you to really appreciate how good you have it.