My state is asking for proof of my non-cash donations. I provided receipts to the charity but now they need documentation of the items donated. What do I provide?

That will probably not be enough.

You are generally required to have reliable written records of you donations that includes enough information about the item to determine its fair market value, such as a description, its condition, and sometimes how and when you bought it.  If you fill out ItsDeductible each time you make a donation, that might be enough.

You also need to show how you determined what the FMV really was.  Again, ItsDeductible might be enough, but since its a black box (you can't say where the values come from) and it's a nationwide value, not local, you could certainly be asked to prove that the ItsDeductible values are reasonable for your items in your particular city or state.

You could also be asked for proof that the items on your ITsDeductible printout were actually donated to the charity, and that you didn't just make up a good sounding list.  

The bottom line is that it depends on the attitude of the particular examiner on the particular day. It'sDeductible is not a guarantee of acceptance, unfortunately.  If you are writing a letter, I would emphasize in the letter that you made your ItsDeductible entries in a timely manner (as you were compiling your items or on the day of donation) as timely or contemporaneous records are usually considered more reliable than records written down from memory afterwards.  You should also include back-up information on values to show that the ItsDeductible values were reasonable for your area -- such as, if you donated to a thrift store, visit the store and see if the prices they put on items are close to the value you claimed.