If you take checks, deposit any checks you may have on the morning of the first business day after the con.
Don’t spend the money without counting it up and calculating the sales tax you’ll need to pay, and making a record of the rest so you can claim it on your income tax reports.
During the con, it’s quite tempting to reach into the cash box and grab money to buy food or pay for the hotel, but this is a bad habit, because it screws up your final tally. If you have to do so, make sure to write a small note with the amount of cash you took and for what reason, and put it in the cash box so you’ll have it at the end of the con and know exactly where all your money went.
Also do an inventory of your merchandise and see what sold, what sold out, and what didn’t sell. Combine that with the notes you took during the con of the items people asked for (because of course you made note of what people asked for, right?), and you’ll start getting an idea of what sort of things you want to focus on making for the next con.
Keep the records of all your sales. Don’t throw them away. You’ll want to refer back to them next year, and the year after, and so on, so you know what sorts of things sell well at this particular con, or in this region of the country.
Then sit back for a week or two and relax before swinging into work for the next con.
Congratulations! You’re now an Artist Alley Veteran!