What foods are safe to eat after expiration date and can I still freeze them for longer use?

Food is good until it is visibly rotting/spoiling, so go ahead and save it any way you can. Expiration dates are changing because so many people are afraid the food has gone bad so they throw it out. And it is still good! Properly canned or bottled foods are good for ages beyond their expiration date. They may not look as appetizing, or be as nutritious, but they can still be eaten safely.
(I consider expiration dates a ploy by manufacturers to get people to throw the food out and then BUY MORE!!!)

Bell Peppers freeze well, the spinach and kale it will change the texture. It would be best to cook them and then freeze them. You can mash the avocado with a little leomn juice and freeze it in a plastic container with a lid.

They could still keep quite well in the refrigerator, personally I wouldn’t freeze them, I would just make a point of using them fresh. What’s the hurry? I’ve never seen fresh vegetables with best before dates on them, it really is up to you to use your common sense in determining whether they are okay or not. If they look fine, then they are fine.

Expiration dates are a scam and more for the stores so you can’t sue them and force you to buy more product. Most everything can be frozen if stored properly and can last up to a year.

Eating most foods past their expiration date isn’t going to kill you.

The only thing I’d be concerned with is dairy products, especially milk. Milk can go bad quickly, so I would never recommend drinking it past its expiration date.