Salmon. Specifically, sockeye. One serving of that has more omega-3 than anything you can stuff in your mouth.
Purslane also has a good amount of omega 3 and loads of other goodness. Best part is that it grows wild in many places.
For my arthritis, I eat sliced beef tendon in hot oil. It’s a traditional Chinese dish that also pretty much cured my painful joints. I went from taking ibuprofen or naproxen all day to walk to not need try any meds at all. I just eat the beef tendon when I get that arthritis twinge and it fixes it.