The night before Thanksgiving
Tonight is, historically, the busiest bar/restaurant/pub night of the entire year. There are several theories as to why, but the one that makes the most sense to me is that people realize they'll do a ton of cooking and baking and table-setting tomorrow, so they want to go out tonight and have SOMEONE ELSE wait on THEM.
So if you go out on the town tonight (and you really should) - be kind and supportive to your server. He or she may actually have dreaded this night for awhile. Basically, don't be a dick.
And, young'uns, take it from your old Uncle Mac56. If you can't afford to tip $1 per drink, every drink - you can't afford to go out.
Now, come tomorrow - If you need to do any business at all on Thanksgiving Day - gas for the car, stop for a coffee, pick up one last ingredient at the grocery - take a minute to thank the person behind the counter for working on Thanksgiving. It doesn't need to be over the top; just something like, "Thanks for working today. You being here makes it easier for us, and we appreciate it."
Finally, here's my all-time favorite Thanksgiving joke =
Why doesn't anyone get laid on Thanksgiving?
Because nobody wants to move all those coats off the bed.