I believe the answer is: Debit Card
To use a debit card, you have to set aside a certain amount of money in an account, and the amount that you can used with your debit card cannot surpass the amount in the account. This would help you stick to your budget and avoid overspending.
A debit card or cash (a debit card acts like cash pulled from your checking account) is the best payment type if you are trying to stick to a budget. This allows for only cash on hand to be used when making a purchase. Sticking to a budget is hard, but it is harder when you have access to a credit card or something that allows you to keep buying without current money on hand. Sticking to cash or a debit card helps you avoid overspending money you don’t actually have.