I lived on the beach right near the basketball courts for 2 years in the '90s and visit LA somewhat frequently, and I wanted to go see my old place and walk the boardwalk to get my kids some T-shirts and something to eat. I'm familiar with Venice, but if you are going to stray more than a couple of blocks from the beach, watch yourself—it’s still a little shady and not recommended to just walk the streets after dark or too far from the touristy places.
I was there around 11am and got free parking on the street; there is an hourly limit to this free parking during the day, and they do ticket, so if you are going to stay more than a couple of hours, go to one of the pay lots.
The boardwalk is the attraction, with one side being the businesses that pay to have a stand and the other side that set up artists, fortune tellers, and other assorted artsy stuff. You should be able to get a pair of sunglasses for $5 to $7 and three T-shirts for $10. They have other assorted paraphernalia and knick-knacks that I grew tired of years ago. It could be fun to shop for hats, blankets, towels, etc., but I was not looking for that.
They must allow bikes on the boardwalk now, but when I was there, they would give tickets to people who rollerbladed or rode bikes in the wrong places. There are also places that rent bikes and rollerblades, and I would recommend going on the bike path that winds along the boardwalk. If you ride toward Santa Monica, you can go out on the pier, and it takes about 20 minutes to ride there. There is limited stuff to see past the pier.
If you need assorted sundries, there are convenience stores that sell beach stuff, as well as beer, but you can get a ticket if you drink in the wrong place. If you need a drink, go to the Sidewalk Cafe (it’s about the middle of the boardwalk, with a big outdoor seating area and awning). There is a full bar and a pretty good menu. The bloody is a good choice.
The beach is big here, and depending on the surf, it’s okay to body surf or boogie board. If you have your shoes, you can get a game of basketball, but to run with the regulars, you need to be lucky, as calling "next game" will probably be ignored. There are three blacktop courts and one new court, at which I did not really look too closely. Over by the basketball courts is a new bathroom facility that was free and clean. It’s a great improvement over the outhouses they used to have.
The muscle-beach area is for members, and I think they offer a daily pass, but I don't know too much about it. This area is closest to 18th Avenue, if you are looking to park near here. I also used to play paddle tennis down here, but the courts were empty when I was here. You can rent paddles down here also, on the boardwalk.
You can people-watch, shop, eat, and get some local culture from the hippies here. I wouldn't think it would be a day-long thing, but some good picture opportunities and memories of a trip to Los Angeles can be had here.