When I'm working in the field, I use a large manila envelope to put all of my receipts in from that event. On the front I put the location of the event I am working and the date I started. I also put my starting mileage.
After the event is over, I close the envelope with all of those receipts and mark the ending date and ending mileage. When I get home I put this envelope in an expandable file folder.
You will often work several events during the year and each will have its own manila envelope with receipts from that event. This keeps them safe until the end of the year when you do your taxes. You will know exactly the mileage you have for the year related to your job and the expenses you had.
Remember you are not reimbursed for these expenses, so you are allowed to deduct these expenses from your gross income. When its time to go to the CPA, he or she will have everything they need to complete your taxes with the proper allowances for you.
What receipts do you need to keep and what expenses can you claim?
All of your hotel bills including the motels you have to stay in to and from the event.
Food expenses away from home.
Any supplies that you buy to do your job to include you computer and printer. (Don't forget your printer paper, ink, folders, pens etc.)
Mileage including the trip to the event, all miles driven related to your job while your there, and the trip home. (Some adjusters prefer to deduct the gas actually used and the maintained on the vehicle instead of just mileage, talk with your CPA to see which is more beneficial to you.)
Toll tickets, parking receipts. Phone cards, cell phones used for your business to include accessories.
Don't forget your expenses for your license and certification, any expenses for continuing education.
Tools such as ladders, tape measures, tool belts, etc.
Uniforms and caps with company logos