Spend a set amount of money per day. If a 10-day trip has a $1,000 budget then logic says any day with over $100 spent will lead to stress and trouble at the end of the trip.
Always keep an emergency stash. Keep a spare credit card and four crisp one hundred dollar bills in different places throughout daypacks, luggage, and with your passport.
Verify expenses before leaving. Items like tickets, transportation, and lodging are easy to confirm beforehand on the Internet or guidebooks. This will help establish a budget before leaving home.
Evaluate each expenditure as necessary, or not. Then compare it to the established daily budget. If earlier days have been below the every day budget then it may be fine to splurge. If the opposite is true, beware.