212:

On line 24 of the 1040, it says "Certain Business Expenses of Reservists..."

There is a separate form (2106) you have to attach, but in a nutshell, you get to show all the expenses you were not reimbursed for, and a portion of it gets deducted from your AGI. There are two categories: Meals and Entertainment, and Other than that.

Example: my unit pays lodging and usually pays travel. However, their reimbursement rate does not equal the federal deduction per mile. So, I show the difference in what I was reimbursed for and what qualifies under the rules. On IDT status where they gave me nothing, I get to claim it all.

On days when you are on IDT status, you don't get per diem. Look up the per diem for your duty location (or, look at a travel voucher when you are on AT status). You can deduct those meals for each IDT day you performed.

Other expenses, such as squadron dues, or uniform expenses: I think uniform costs are in the clear; I am less certain about dues.

I didn't know about this deduction until 3 years ago; it has saved me a bundle since.