Most of the solutions we use in daily life are simple, but few are elegant. I consider a solution elegant if it's simple and you become conscious of it, like "hey, that was a really cool solution to the problem."
1. Efficient spray bottles
You know that pipe that goes down from the spray nozzle? Some companies have extended it all the way to a corner of the bottle, so you can spray out almost every drop of liquid.
2. Toilet paper dispensers
Most of them have this bar and spring mechanism that can be tricky to remove and install correctly. Newer ones flip up like a drawbridge, making toilet paper rolls easy to change.
3. Keeping cabinets closed with rubber bands
When I had babies in the house, one danger in the kitchen was that the kids could open cabinet doors and get at the dangerous things inside. Instead of buying complicated locking mechanisms to install, we just strung a rubber band across the handles. It was easy for us to remove to open the cabinet, but difficult for 1 or 2 year olds to figure out.
4. Keeping the cutting board in place
It's kind of dangerous when you're cutting something and the cutting board slips. To prevent this, I put two or three rubber bands under the cutting board.
5. Removing tight twist off caps
One more rubber band trick... if you have trouble opening a jar, just put a rubber band around the edge of the lid. It will be much easier to open because you can get a tighter grip. Companies should rubberize the edge of their caps and lids!
6. Vacant/Occupied flag when you lock a restroom door
I'm surprised this isn't more common. At least have a red or green dot.
7. Vacant/Occupied flag visible from a distance
I see these at the Costco gas pumps, parking garages, and for airplane restrooms. They're very helpful. Maybe they should put them at the top of all restrooms, for those moments when you're in the middle of dinner at a restaurant and need to use the restroom, only to get out of your seat, walk to the restroom, and realize it's occupied.
8. The lid lock on top of the Instant Pot
It's such an elegant solution. There's a sliding piece of metal that moves up and locks the lid when the Instant Pot is pressurized. When it's not pressurized, the piece falls in and unlocks the lid.
9. Your phone
When you think about it, your phone is a simple solution to a big problem in the 1980's and 90's. Everyone had lots of neat electronic gadgets, but to carry them all with you was a huge hassle. People carried around watches, keys, loyalty cards, photographs, cash, flashlights, notebooks, pens, cameras, camcorders, boomboxes, MP3 players, GPS devices, etc... until smartphones integrated them all into one device.
10. Google Search
Before google search, the internet was fragmented. People found things through internet directories and specialized search engines that each had their own blind spots and strengths. Then Google came along and let people type whatever they're looking for in the search box without any special syntax or consideration, and it would try to find it for you.