I would say to only bother keeping the ones you know you'll use for itemized deductions. This includes any unreimbursed business expenses and vehicle licensing fees. There are a lot of other itemized tax deductions possible, but those are two common ones.
Also, keep track of your business mileage (mileage before and after the trip, and commuting doesn't count as "business mileage"). You may also want to keep receipts of all out-of-state purchases if your state is one of those that tries to collect state tax on out-of-state purchases. Ensure your supported charities are 501(c)(3), and they'll give you a receipt at the end of the year.
Don't bother keeping fast food or gas receipts (unless they're business expenses).