Pay for Some of the Bigger Expenses Before You Leave
Unless the trip is a spontaneous one, this is generally the easiest to do with flights. I also try to make sure hotel or AirBnB costs are already paid off by the time the trip arrives. In addition, I sometimes purchase tickets to museums or shows before the trip. By spreading out the expenses over a few months, I don't have to dread the gigantic credit card bill after I return, because the big expenses were paid off before I left.

Try to Operate on a Cash Budget for Some of Your Spending
Generally, I do this with food and admission fees to museums or attractions. It enables me to set a reasonable budget before I leave, and because I have physical money in my hands, it keeps the spending in check. When the wad is getting thin, I know to ease up on expensive meals or frivolous spending. I still use cards for most of my shopping and often one big, blow out meal at a restaurant I've been dying to try toward the end of the trip.

Be Aware of International Fees on Your Cards
Typically the fees are small, only 3 or 4%, but I resent the extra charge on principal. Why am I paying a tax on my spending in the States (for example) when the credit card company is an American one in the first place? It bugs me. Earlier this year, I applied for an Amazon Visa specifically because they don't charge surplus fees for international spending.

Have a General Plan in Mind and Know Rough Prices in Advance
When I create an itinerary for my trips (hello, type A!), I always include prices. If it's a restaurant, I put the price range of a main dish, for attractions, the price of an adult ticket. Sometimes I have a list of various options for a day rather than a strictly-followed itinerary, but regardless, I have a pretty good gauge on what something is going to cost me before I dive in.

Don't Feel You Can't Be Spontaneous
As long as I'm responsible with my budgeting for the most part, and spontaneous spending isn't a daily or hourly occurrence, I feel it's more than fine to spend money on something without meticulously planning in advance. The whole point of being responsible with my money is getting to be irresponsible every once and awhile without feeling guilty about it ;)

If you have any other tips or techniques when it comes to money and travel, feel free to add them in the comments! I always love to hear from you!