Where are you staying? What kind of food do you like? Golds charges $20 for a day pass, if you're a member at another Golds you can get a visitor pass from your current gym to get you in for free. Golds is usually pretty quiet late at night, so go after 1 pm or earlier in the morning like 9 or 10. I hardly see anyone working out a muscle beach, but it would probably be fun to try out.
Venice has dirty spots. If you want to see a nice beach go to Manhattan, Hermosa, or Huntington. There's places to eat all over LA that have been around awhile. The Griddle has the biggest and best pancakes I've ever eaten, plus you may be able to see a celebrity. Of course there's In-nout, pinks hot dogs, tommy burgers, a nice burger and beer place in santa monica is Fathers Office.