1. Beware of travel visas and reciprocity fees
Before you travel abroad, check the entry/exit requirements for the countries you're visiting. These little fees can blow your budget big time, because sometimes they're not so small. Many times exit fees are rolled into your airline ticket, but entry fees are not. You've got to know when and where you'll be charged.
For example, Argentina charges a $160 fee if you fly into Buenos Aires, but nothing if you cross over the border in Chile. Brazil will turn you away if you haven't gotten a visa (not cheap) prior to arrival. Most countries let you stay 90 days, but for some it's only 30 and if you overstay, it'll cost you. Before you go, check it out.
2. Withdraw the maximum funds from the ATM
Some of you may be saying, I don't want to carry around that much money. It's not that much. Most US ATMs have a limit of $200-300 per day, in other countries it can be much less.
Taking out the maximum amount will save you from getting tagged with multiple ATM fees, your bank fees, and international transaction fees. Plus the exchange rate is better than any you'll find on the street. As a budget traveler, I'd figure out about how much I would need for a week, withdraw that and keep the majority stashed in a money belt.
3. Stay in hostels
I hear this all the time, Ewww ick - hostels are for hippies and college kids. But it's just not true (mostly). The majority of hostels have private rooms. They're more expensive than dorm style, but far cheaper than a hotel. However, the real magic of staying in a hostel lies in the people you'll meet and the tips you'll get about where to go and what to see, most of which will be budget minded. Trust me, these insider treats aren't going to find you at the Four Seasons.
4. Couch Surf (No, it's not an aquatic endeavor)
If you're adventurous and want to see a place from the perspective of a local, check into CouchSurfing.org. It's an amazing program that pairs travelers with locals who open their homes to fellow sojourners. There's no nightly fee, but payment in the form of cooking, doing the dishes or sharing your talents (whatever they may be) is encouraged. It's safe. It's fun. And it's cheap!
5. Make friends with the grocery store
Eating out is expensive, no matter what country you're in. But you can save a chunk of change if you buy food from the grocery store. Not only will this save you money, but it can also be an absolute adventure into unknown culinary territory. Grocery shopping in Tokyo is the safest game of roulette you'll ever play. Have fun with it!
6. Wheels, wings or rails?
With so many transportation options, which do you pick? First, I'll never buy a ticket (besides my arrival/departure ticket) in advance. Plans change. It's the best part of travel and if you're cemented into a ticket you'll either pay to change it or regret that you have to keep it. Both options make for a less than awesome experience.
Stop thinking you have to fly everywhere. The bus system in South America is part of the culture and it's not uncommon to take an 18-27 hour bus ride in a coach that's outfitted like a first class cabin. I've done it and it's rather pleasant. However, flying in Europe can be cheaper than taking multiple rails. Don't trap yourself into one mode of transport. They've all got their attributes.
7. Pack a full suitcase
This may not work for everyone (some of you will just buy another bag, tsk). But if your suitcase is full, you can't put anything else in it, which means you can't buy unnecessary baubles along your journey.
If you've budgeted baubles then only leave some room. Not a ton. I can honestly say the travel trinkets I've collected over the years can be counted on two hands. Bottom line is, while a choice item or two that sings to you is well worth having, you don't need to buy a lot and the items you do buy will be all the more memorable.
8. Turn your data off
There are international phone plans, yes. They are also pre-unlimited-calling-get-off-the-land-line-you're-costing-me-$1.25-a-minute expensive. Plus they don't work in every country.
BONUS: Smartphone Travel tips
So how do we keep in touch with home without blowing the budget? Most of us have smart phones, and almost everywhere has Wi-Fi. My personal favorite is Skype. If you have the app installed on your phone you can call another Skype user for free or a phone number for a few cents a minute.
Another free calling app is Viber. It sends texts, pictures, and calls anywhere for free between fellow Viber users. There's about a 10-minute call limit before it cuts you off and you'll have to call back. Tricky, Viber, very tricky.
If you have clients that need to stay in touch. Forward your phone to a Google Voice number. There you'll receive transcripted voice messages.
Part of travel is removing yourself from normal life, so you don't really need instantaneous access to everyone via telephone. With these options you can stay in touch with those who matter without breaking the bank.