I donated food and supplies to an animal rescue throughout 2016.

[lawright]

Which category do I choose for how I valued these donations? I have receipts where I purchased the food and supplies

[Hal_Al]

If items were purchased for the purpose of donating them, you treat it as a cash donation. Your purchase receipts may  be acceptable in case of an IRS audit, but ideally you get an acknowledgement receipt from the charity. A receipt from the charity is a must if the value was more than $250.