As has been said, whether you get a 1099 or not, you should ethically report what you make as income. Considering how important integrity is to our industry, I would hope that people would retain that same integrity on and off the field.
Personally, I think I have only ever gotten one 1099 per year and only accounts for a small portion of my game fees.
So to be on top of the recordkeeping, I have a log book (small moleskin notebook) with everything I do for officiating.
When I go to a chapter meeting, committee meeting, recruiting events, etc., I capture one-way mileage from my house to the meeting. (For chapter meetings, since we have them all at the same place, it is always 12 miles 1-way for me).
When I go to a game, I record date, # of games, what position I worked, and one-way mileage to the site. When I get the check in the mail, I write how much I got paid and my tithe on that game check.
At the end of the year, I can quickly calculate my total mileage. (In 2017, I captured a total of 1628 miles.) Since I own my car outright, I can deduct depreciation on my car as well as mileage. TurboTax does a lot of these calculations for me since I've been doing it for a few years.
Any new uniforms/equipment each year is deducted, but this is usually small relative to...(see below).
As a young(er) official who aspires to working in the college ranks, I also deduct cost of clinics/camps and all related travel expenses. One camp at 500-700 bucks, plus hotel, mileage and meals will more than offset all my HS sub-varsity and varsity income for the entire season. Over time, the IRS might begin to look at this if I have several years of net negative operating expenses...however, as long as I can show that I am progressing towards a goal of one day working D1 ball, then I am not worried about answering those questions during any potential audit.
For UIL games there is travel pay included as part of our invoice we submit. If we are paid the travel fee we can't deduct mileage to/from that game can we? I only ask as I did not claim any of my mileage for UIL games where I received travel payment included.
My understanding is that the mileage paid is treated as income, and then deducted through your business expenses. Since schools don't split out line items for game fee and travel expenses, I just treat the full check as my game fee and recoop the travel expenses when I do my itemized deductions. Of course, that said, with the passage of the tax reform bill, it will take a much higher threshold of deductions to itemize on next year's taxes. (standard deduction is doubled up to 24k from 12k for married filing jointly).