I find that doing a lot of research before the trip helps tremendously. For example: are there washing machines available at the hotel, for guests to use? If so, bring some detergent pods and you can travel lighter and do a load or two while you’re staying in the hotel. You can also buy detergent in a store when you are at the location, but if you have it in advance, you are likely to have paid less for it (rather than buying it in a tourist trap store which charges higher prices). That’s just one example.
As far as spending, I tend to be fairly frugal and consider anything I spend on as far as meals or tickets to be part of the cost of the trip. Sometimes I may buy a package (for example, there’s something called “City Pass” which is available for many cities in the US, and it is comprised of tickets/admission for five or six things). Even if I don’t use everything in the package, still, if I use ⅔ of it, it still comes out to be cheaper than if I paid individually for the different things I did use.