There are a couple right off of I-80 where it crosses I-5. My book is down in my truck right now. I will bring it up a little later.

If you're looking to stay near 5, Woodson Bridge is probably your best bet. I've never camped at any of these - but I did find Colusa-Sacramento and Woodson Bridge in my book of the 50 best places to hike in northern California.
I live in Redding, so it would be fairly easy for me to get more info on these, or the ones I posted earlier, if you like.

interesting, i was just at some of these places to scout them out for future camping. i visited san luis state rec and hatfield.

san luis is conveniently located at san luis reservoir in the rolling and already golden hills on the coastal side of the valley near los banos, I-5 and cali hwy 152. there are 4 campgrounds around the area; 3 of the 4 are away from the highways. i didn't visit the one that sits close the hwys.

- san luis creek campground is back in the hills, 2 loops of sites, each with a tree, table, and ring. bathrooms and showers, swimming at the beach, camp host, fishing. water avail.
- bassalt campground is back in the hills, away from water but with much more shade in many areas. bathrooms, showers, camp host. swimming not encouraged in the main reservoir as the cut-off from shallow to deep is sudden. fishing. water avail.
- los banos creek campground is waaaayyyyyy back in the hills, you don't know that the little reservoir is there until you're almost on top of it. very secluded with maybe 15 campsites, many with shade, all with table and ring, porta-poties only, swimming is right in front of you, fishing. if you're looking for an easy place just passing by, this likely isn't the campground for you (but it looks fun!). dunno about water avail.

the other place was hatfield state rec area, small, some traffic nearby, not a lot on the road it actually is on. no specific "campsites" per se. there are two parking lots and several large groves that have tables and rings under them. stake out your table and ring and camp right there. not possible to pull up to your campsite, but the distance from car to site is 15-75 feet. easy. and beautiful too, with all the old maples and oaks. right on the merced river, swimming allowed? bathrooms, showers? unfortunately mosquitoes rule this time of year, the park is right near the confluence of the merced and san joaquin rivers.

for you, i would say san luis creek campground is easiest. $20 i think.

www.parks.ca.gov/

search by name

cheers, good luck