Grocery stores are busiest on weekends and after work during the week. Avoid those times! Whenever possible try to shop early mornings or late at night if you want to avoid crowds.
It might take a few tries to find the optimal grocery shopping time for you.
I have found that the HEB near me in San Antonio is not busy before noon on weekdays and after 9pm. Publix isn’t too busy after 7pm in Naples.
Costco is pretty busy during the day even on weekdays, mainly because there are samples offered. After 5pm or so the samples go away and you are there before the dinner people.
Trader Joes always seems busy! In San Antonio, I haven’t found a great time to go yet. In Naples I found that going right before they close isn’t as busy.
Tip: Don’t shop right before holidays! It will be busy no matter what time you go, unless you can make it right when they open or right before they close.