If you have a hull, engine, paddles & lifejackets, you have the minimum (bar a tank of fuel & your lunch!) for a day out!
Other stuff that might be useful are a couple of long-ish ropes & a small anchor. Not maybe as important if you are staying inland, as you will always be blown ashore! A dry bag to keep the layers of clothes you might need later, or have removed as the day gets hotter is also a handy thing and it also keeps your sarnies / tent dry!
As for launching, if you mean the Aberdeen area, the likes of Spartacus might be better placed to advise. If you plan to go, camp & SIB, let us know where your favourite areas are, as there are hundreds of places you could play that sort of game.