In years where money has been tighter I've gotten stuff the kids need for at least part of the gifts. So, for example, gloves, pajamas, slippers, backpacks, hoodies, hats, sports equipment, musical instruments, books and workbooks. But all of it more fun than usual. Or if we're doing something special over winter break (the circus, say) we'll give that to them as a gift.
We'll also let them choose an app up to a certain dollar limit (say $5).
To be honest, both their grandmas go kind of crazy. Even in years where things are more comfortable we try not to go too overboard and get them lots of crap. I try to think really hard about what interests them or enriches them and get that. And I try to keep the spending down.
One year I took a big old plastic shoe box, decorated the cover with their names and wrapped the box and some art supplies - paint, brushes, palettes, paper, sponges - separately. They loved it and it was useful for years.