If you are travelling with budgetary constraints, start your trip out on the right foot by using a price comparison website online. You can often even get discounts if you look around. Expedia coupons are a great way to get an instant discount and they're easy to find.
Figure out what your destination is like and then keep that in mind as you decide which things you'll need on your trip. If you are going to a cold climate and your child has never experienced that, you will need to get climate appropriate clothing. If your swimming suit is in tatters and you are headed to Hawaii, then take care of that ahead of time. Being prepared means you have the luxury to shop around and get exactly what you want for the price you want to pay for it. If you see a fabulous but expensive swimming suit in your hotel's boutique, you can get it if you truly want it and believe it is worth the price, but you won't be unduly pressured into getting it out of necessity.
Know what you want to spend your money on. Are you a foodie who wants to eat at that celebrity chef's restaurant? Then plan for it and its cost. Find local places with great food for very little. Perhaps eating two low cost meals makes room in your budget for glamorous dinners. Make your priorities lead your actions. Don't let being flustered or unprepared control your experience.