The list of things you can do with a 12x16" travel poly fill pillow is long. And don't forget to buy the machine washable cases, or, in addition to dirty pillows, you'll eventually deal with burst seams and pieces of fill everywhere. Foam pieces at similar sizes (check your local foam store or on line) can serve many of the same purposes.
Bed: Put one under each elbow for anyone who sleeps with bent elbows (e.g. hands resting on the chest). You can use them under wrists as well, depending on the need.
Put one under each knee and/or ankle. If pressure ulcers are a real concern, use Prevalon or similar boots rather than ankle pillows.
Wheelchair or recliner: Put one on the headrest for softer neck support. Put one between the body and each arm rest or lateral support, for more cushioning. If just a little lumbar support is needed, put one behind the lower or upper back.
Put one on each recliner arm rest for more support, and/or on a recliner or wheelchair lap tray, to support the elbows and/or forearms while working or reading.
An e-reader or tablet can also be supported/positioned with foam and/or pillows. Use bungee cords if/as you need them.
On a wheelchair foot rest, one or two can provide additional cushioning for bare or socked feet; however, a single piece of foam or a gel pillow works better long term.
Commode chair: Insert one between the body and each arm rest, for extra lateral support and/or softer arm support.
Computer table: Depending on your setup, can be arm, leg or equipment support (don't obstruct ventilation).