I’m currently underemployed and may be looking at having some time to fill over the holidays when most people would be busy with family obligations, etc. However, I don’t relish the idea of working a cash register, nor do I really have any experience in that area. Are there other options I’m not thinking of?
Retail seasonal work often is not cashiering, but stocking shelves.
Flower shops often hire extra delivery drivers from now through Valentines day.
Last year when an unemployed friend was living with me, we found several seasonal opportunities on craiglslist for places like factories, warehouses and shipping centers.
You you mean Christmas season… A lot of resort areas do seasonal hiring during their busy season.
Winter… ski resorts?
The post office often hires seasonal warehouse/dock workers. Most of these are laid off again at the end of the holidays, but a few are sometimes retained as regular employees.
There’s always playing Santa at your local mall or department store.
Tax preparation services.
ETA: maybe not, didn’t read the timeframe in the OP closely.
UPS definitely hires seasonal workers.
Ken Jennings might say FedEx, but H&R Block is the number one seasonal employer.
Only the OP asked about holiday seasonal employment.
The local IRS office advertises for seasonal data transcribers here in Austin.
I’d check delivery companies (UPS/FedEx). Maybe look for a Christmas tree farm. I know the one around here hires part timers.
The tax season falls squarely around the President’s Day holiday and also includes Easter and Valentine’s. 
Also April Fool’s, if you do it up big that time of year.
There’s “landscape” work in the form of hanging Christmas lights, giant wreaths, “winter interest” displays in planters (evergreen boughs, redtwig dogwood branches etc) and that sort of thing. Living in a snowy area helps since, if you can grow flowers in December, you probably don’t need a porch planter full of pine boughs. I spent a couple months on a ladder with a long hooked pole hanging lights on 60’ spruce trees owned by people with fancy homes.
I’m talking mainly at the private level since towns tend to have their maintenance departments hang the lights along Main St.
Big catalog companies like L.L. Bean and Lands End bring in extra phone farm workers for the holidays.
I had friends in college who would get jobs with UPS every holiday season, loading trucks.
One Christmas season many moons ago I worked at a jewelry store at the mall wrapping gifts.
On edit: No doubt department stores, mall management companies, and other places also offer similar employment. If such places offer gift wrapping to the general public, well, that can’t too easily be outsourced
And let’s not forget snow plowing…
For a short-term, though perhaps a crappy job, check this.