The most challenging part for most people planning a trip is a budget. Plan a trip properly and you could save quite a bit of money on it. Problem is that many people skip planning and buy everything on a spot, where there are tourist traps everywhere. Here is my general advice on how to save money while you travel.
Buy in bulk
Buy bottle packs instead of individual water bottles. I've only discovered that after many-many road trips that water is quite a big expense since in tourist destinations it might cost 2$ or more per bottle (if you have 4 people in your family that's 8$ right away). Instead, buy a pack of water. It would cost much cheaper than individual bottles and would serve you multiple days
Buy snacks at the grocery store before going to tourist areas. Seriously, you would probably want to have some mid-lunch or mid-dinner hunger and if you don't have snacks most likely you are going to end up paying for some expensive restaurant. Snacks would save you some money.
Buy lodging (hotels/motels) out of the downtown areas to save money. If you get some great deal on lodging in the downtown area - fine, but if you don't I would recommend buying a hotel in some inexpensive area out of downtown or another city close by.
Buy tickets in advance
Buy attraction tickets in advance or buy multi-attraction tickets. Try to avoid tourist traps as much as possible (if you can). Tourist traps are designed to take money out of you, but food and goods there is usually much worse value than in other areas of town. Think twice before purchasing something there.
Travel on weekdays
Weekends are a time where most people are travel. What is the best way to do something smart? You guessed right - do opposite of what other people do to save some money. Also, traffic to popular destinations is usually way less than on weekends.
Safe travels! And remember - the less you spend on travel, the more days out of vacation you can afford. Which means even more travel plans in the end.