This post covers Warsash to Swanwick and back.
Launch point: Public slipway opposite the Rising Sun.
Parking: Shore Road Car Park (outside the pub), Passage Lane Car Park - Both car parks are usually free in the summer with a duration limit, but gives you enough time to get out for a decent paddle without having to rush. Gets busy though, especially given the popularity of SUP these days.
Check tides and wind as usual. I try to time it so the current takes me up to Swanwick on the rising tide and back out on the ebb tide, but so far miscalculated it so that getting back to Warsash is usually a bit more work.
This is usually a nice gentle paddle up and down river, checking out all the boats moored up along the way. There's SUP hire now next to Swanwick Shore Road Car Park, which is excellent as it means you can disembark and grab a coffee for a bit of a break. Another option is paddling across the river to the Jolly Sailor for a swift one before heading back down-river, or stopping in Hamble.
If you're feeling very keen you could continue up the river further to the Horse & Jockey in Curbridge, but I'm usually OK doing this mini-paddle.
Doing the same route in reverse works well, but Swanwick Shore Road Car Park is usually packed with SUP'pers and kayakers so you really have to get there early (assuming tides and wind are sensible).