I keep a detailed spreadsheet for each month of shops that I have done. It lists the following info in columns across the top:
DEBRIEF CODE (One MSC uses hexadecimal codes to debrief all shops)
INVOICE NBR - PAYPAL
Then I list every shop I have scheduled for the month. If I have a route scheduled, I merge the individual lines for mileage and non-reimbursable employee expenses (food, office supplies, etc.). At the bottom of the list I list each MSC that I have shopped with and using Excel formulas, I compute how many shops I have done for them and total the costs, fees paid, fees owed and taxable amounts for each and a grand total for all for the month.
When tax time comes as it is now, I can simply do my calculations for what each company paid me for the tax year and correlate those against the 1099's I received from companies who paid me more than $600. I can also compute the mileage and expenses that I incurred on my shops for the Schedule C information.
Several advantages of this type of detailed information on a spreadsheet is that it is ongoing, you keep up with it weekly, if not daily and if, God forbid, you should be audited by the IRS you have a viable record to justify your return. And you can use it to track your payments from each MSC to find out if a certain shop was not paid, was not paid in full and which MSC's are delinquent in paying you. And you can copy and paste the data when you contact them showing the shops you have completed, the fees and expenses that are due you, etc.
If anyone needs help using the formula features of Excel, I will be happy to assist. I have learned through trial and error and I am still learning.
Side note: I am rather anal retentive so I also use spreadsheets to keep databases of my most frequently shopped locations. I have lists of post offices, grocery stores, restaurants, gas stations and retail stores. This way I already have the information I need including the full addresses, phone numbers, site ID's, fees involved, etc. When I get a job assignment, I simply peruse the applicable database and copy/paste the line item from the database into that particular month's spreadsheet and change the shop ID, due dates and planned shop dates to match the current assignment. If I get a new assignment that I have never done before, I enter it in my monthly worksheet and I also enter it in the applicable database file for future reference.
IMPORTANT: Save the contents of your spreadsheet often and keep a copy of it on a flash drive. It will become one of your most prized files. Excel will automatically do a backup of the file every 10 minutes or so so you can recover some of your changes in the event of a system crash or power outage but I try to backup the database after entering new shops and anytime I make changes to the file. Get in the habit of doing this, folks and it will save you a lot of headaches and angst.
One buzzard to another while circling high overhead (paraphrased), "Patience hell! I want to shop somewhere."