@Bendboater
I guess you could hike into Black Canyon (just below Hoover Dam) from quite a few places (I'm sure there are even technical routes into it) and then packraft to a camping beach. Eventually you'd paddle to Willow Beach where you can leave a car. Non tech routes into it are very, very popular, and you won't be alone. These would include White Rock Canyon, on the Arizona side, and Goldstrike Canyon on the Nevada side. I recommend weekdays for these hikes. Otherwise every punk kid from Vegas will be there. If you are into real canyoneering, do your own research, I don't know those routes, but I'm sure they do exist. In any case, when you find yourself at the river, you would then use your packraft to get to Willow Beach boat ramp.
Goldstrike:
https://hikearizona.com/decoder.php?ZTN=2402
Whiterock:
https://hikearizona.com/decoder.php?ZTN=422
Below Willow Beach is lake Mohave, which has a wild shoreline. You could hike into it, but then you'd be faced with paddling a packraft on a windy lake. It's beautiful, though.
Further on downriver, by I-40 bridge, you can get into Topock Gorge via various non-trail routes on either the Arizona or California side. Be aware that where the washes run into the river there is generally always very thick brush, making access difficult.
It just seems a lot more practical to me to start with a kayak and go downriver, pull in and do your hikes, and then find yourself a campsite. It's illegal to camp in Topock Gorge, though. You can go on down to Lake Havasu and camp or take out, but it would be awfully slow in a pack raft. Again, having a nice swift kayak would be more practical. Put in at Topock 66 Marina, take out at Castle Rock Bay or go all the way to Parker Dam, which is about a three or four-day kayak trip.
On the south end of Lake Havasu on the Arizona side the vehicle access is restricted from the lakeshore, which has cliffs and steep hills. Along here are dozens of boat-in campsites that can also be used by backpackers. There are informal trails all along that area which are rarely used. These boat-in campsites have pit toilets and picnic tables. On the other hand, if you're backpacking, you wouldn't need to camp in a pay campsite. I've often thought of backpacking along that end of the lake. Just haven't gotten around to it. Take along your water filter. The lake water is very clear and filterable.
There are many, many sections of the lower Colorado that have houses lining the riverbank, or other private property taken up by farm fields. And there's a big Indian Reservation which has lots of no trespassing signs. You have river access, but aren't supposed to land. Between Highway 62 bridge in Parker, and Mayflower Park in Blythe I camped at two CA-side RV parks in a 55-mile stretch of river. There were no other legal places to camp--it's all levees and farm fields on the Indian Reservation.
Downriver from Blythe there is easy access. In that area you could ride a bicycle or drive a pickup along the river levees for miles, (both sides of the river) and camp on beaches, but there are no canyons. It's flat. There are farms there. Kayaking through there, we found random beaches to camp on, plus an RV park (MacIntyre), and a federal campground (Oxbow Lake). All were accessible by vehicle as well.
Downriver from Walter's Camp (near Palo Verde CA) you get to the two wildlife refuges which are best reached via kayak, canoe or motorboat. Walter's Camp is the put-in. You don't get any camping places at all until you get to Picacho State Rec Area on the California side. Otherwise, no camping is allowed in the refuges. From the put-in at Walter's Camp to the very first campsite is a whopping 17 miles of paddling. I wouldn't want to do that in a little inflatable, but it's not hard in a canoe or kayak. Also, access to the river via hiking in this section is most often impossible due to it being marshland with thick reeds.
Anyway, these are just some areas I know about. Hope this is helpful.