We did a 3 day, last minute trip to what is very likely the most popular "long weekend destination" in California. Consequently, we spent most of our time in bumper to bumper traffic both outside and inside (!) the national parks. When we were not stuck in traffic, we were going round in circles looking for a place to park.
In spite of all that, it was 3 days well spent, out in the open (at least the times when we were not in the car)
The next time we do this, we decided that the only way to enjoy Sequoia is to camp by the river, just sit back and relax. This means planning and booking campsites. This time we didn't plan in advance and we also missed visiting Moro Rock and Crystal Cave (which I'd done in a previous trip).
If you don't go camping and are just visiting, remember to carry lunch with you. The delis/restaurants are at one end of the main road. If you don't carry something with you, it'll be late afternoon by the time you reach the visitor area that has the deli, which is near the river campsite.
Also, if you like Thai food, don't miss dining at this little restaurant called Thai Basil in Visalia. The food is excellent and beats any South Bay Thai place hands down.
Now, Yosemite requires one long, multi-day trip or multiple short trips. We did neither and chose the worst time to visit, which is any long weekend. It looked like the whole of Silicon Valley was in Yosemite Valley.
Again, remember to carry lunch with you. It gives you the freedom to pull out of traffic at Bridal Veil falls or Cathedral Beach and enjoy lunch instead of waiting in traffic. The only place to buy lunch in the park is in the Yosemite Lodge area or Curry Village. And both places have mostly pizza and not much else.
If you go during Summer/late Spring, remember to carry mosquito repellant (ouch!). Very useful if you want to hang out near streams and Mirror Lake (Why would you not?).
We also spotted a mama bear with cub just outside Yosemite. The photo is not very clear though.
Until next time!