snobahr

I can't answer for flea market stuff specifically, but in my experience:

• Have your paperwork in order BEFORE arriving. Resell permit, local business license if applicable, whatever the venue demands of its vendors.
• Have at least one other (reliable!) person with you, so you can go use the restroom as needed.
• Bring a cooler full of bottled water and snacks (use reusable icepacks instead of loose ice, too - reduces drippiness/mess - the venue will thank you for not leaving a mess, afterwards!).
• Bring a banker's box-sized plastic box (rather than cardboard) to hold your business-side paperwork in: handwritten receipt book, pens, box of tissue, roll of paper towel, business cards, sunscreen, bandaids, roll of duct tape, a couple of small trash bags
• If you're going to take plastic, a fully-charged battery pack for your smart device, and make certain your card unit works, and that you have the data available for a day's worth of transactions
• If you're going to be cash-only, have sufficient change on your person to make change.
• If you're using a folding table to display your wares, a tablecloth for hiding whatever you stash underneath (assuming you want to put empty boxes/overstock under the table).
• If you're going to use a canopy of any sort, some manner of weights to keep the wind from blowing it away.
• In your inventory, decide what your absolute, rock-bottom price is for things, and mark them up at least twice that, and allow yourself to be haggled down. If things sell at their stated price, WOO HOO!
• If you have the space to do so at home, set up your booth area before you go to the market, to figure out the best way to display your stuff, to make sure your stuff will fit in whatever designated size the venue permits.
• A comfy folding chair

Remember that everyone at the market place is as human as you are. It costs you nothing to be polite and patient, regardless of how crappy a day your customer(s) might be having - try not to contribute to how crappy it might be.

Some venues permit retailers to set up booths. Retailers need business licenses/Tax IDs. Look up what's necessary in your area.

How long have you been a Santa? Did you go to one of the Santa Schools? Was your suit custom made for you, or was it OTR?

I can't get the link to open (I'm using an adblocker, and the site doesn't like them). Are you more interested in the wax or the honey?