We all use the phrase "Don't nickel and dime me" and I am here to tell you that those nickels can really add up in a remodel project. SET A BUDGET. Set a construction budget for a remodel, try to think of every piece you will need. If you are doing the work yourself, make a list of everything down to the nails, if you are hiring someone to do the work, make sure you walk through with them and get a concise, detailed bid.
As a homeowner, a real estate investor and even as a contractor I can tell you that many times in a remodel of a home the nickels are what get you. The quick trips to the hardware store, the extras, the $50 receipts here and there add up to real money quickly.
Be prepared, have a budget line for unexpected items and stick to your budget. Like any budget, line items should be fluid, while the top (budget number) should be solid. Prepare to take money away from one line to help balance others. Maybe you can live without the wallpaper for now but you can't live without getting that mold removed that you found.