I always make them with a specific recipient in mind.
What do your guests like and how old are they?
DS plays guitar so he has had personalised plectrums and personalised leather key ring plectrum holder from etsy, guitar cleaner etc He also loves bath bombs, aftershave etc
DD loves cooking so has had a little silicone crab spoon holder, nutmeg grater etc or earrings, mini perfume, make up/nail polish/facepacks.
DM loves gardening and scented candles so she has had things like unusual seeds (black tomatoes, micro tomatoes, grey poppies) small bulbs, mini candles, coloured garden twine and plant labels. She also loves unusual earrings.
I won't go through my entire family but maybe there are some ideas!
I usually add a scratchcard (although we agree to share any big wins!) and everybody's favourite wrapped penny sweets to fill the entire space. It makes the crackers a bit of an event now that everyone is adult and Christmas is a bit more staid than with young DC 