donating grave sites to a veterans' group

That would be a charitable deduction but you must itemize to use it. 

You may have difficulty determining the fair market value.  If you owned the sites less than 1 year, your deduction value is the FMV on the date the previous owners died.  If you have owned them more than 1 year, the donation value is the FMV at time of donation.  Keep records of how you determined the value.  If the value is more than $5000, you need an appraisal, and you need to file with your tax return, a copy of form 8283 that is signed by the appraiser and by an authorized representative of the charity.  See publication 526.

https://www.irs.gov/pub/irs-pdf/p526.pdf

In order to deduct the contribution, the veterans' group has to be authorized by the IRS to accept tax-deductible contributions. Ask them if they have a "determination letter" from the IRS, or look up the group using the Search for Tax Exempt Organizations on the IRS web site.

Donations to charity are an itemized deduction. They will not reduce your tax or increase your refund unless your total itemized deductions are more than your standard deduction.

also check the tax-exempt status of the organization. not all are registered as charitable organizations.

if it is it would likely have one of the following as its tax-exempt status

501 (c)(2)

""""""""(4)

""""""""(7)

""""""""(8)

"""""""(10)

"""""""(19)

"""""""(23)