Formal dining: remold the sand to conform to the fine china, and not a bit of it will even think about falling off the table.
Non-gaming parlor entertainment: flatten out the center section...packing it down hard. Dig a hole at each corner and one equidistant down the 2 longest sides. Play pool. Bonus: you can repair a gouge in seconds.
Non-gaming sports: practice getting out of sand traps, even when its storming outside!
The only time we played on a sand table (my second OD&D group), the DM would flip the massive plywood lids onto his table and we would use it as a regular table. A few times there were whole miniature battles going on in there that we'd look at prior to game setup.