Keeping track of incoming and outgoing money is important and one of the areas most often overlooked by a new business. In the beginning when things may be slow it's tempting to think you can keep track of your expenses in your head or on a piece of paper with receipts in a folder. By the time you realize that plan isn't going to work, you're behind in keeping track and now stuck trying to fix your methods on the go. .
Do it right from the beginning. If you have an accountant that will be doing the taxes for your business, ask him what numbers he will need to do your taxes, and make sure your accounting procedures keep track of those numbers. Some shopping cart software comes with accounting software built in. If yours does not, get yourself a small business accounting program like Quickbooks or Peachtree, or create a detailed spreadsheet. Set up your expenses and income, and create detailed categories. Make sure your accounting procedures that you set up in the beginning will continue to work when you are getting 50+ orders a day and multiple deliveries from different vendors.