Large items are pretty easy to predict. You aren't going to buy a bathroom vanity, then rent a truck to take it home and then realize you needed two vanities.

Large items are pretty easy to predict. You aren't going to buy a bathroom vanity, then rent a truck to take it home and then realize you needed two vanities. If you are buying wood you can measure the size of the wall. Estimate the studs you need based on 16" gaps. Buy that much plus a few extras. The constant trips back and forth to home depot is generally smaller items that you forget. You need a special socket size, you need a different type of nail, etc.