Some charts, depth sounder and if possible a cheap plotter. There's some cracking rocks in Belhaven Bay and off Tyninghame that are best avoided
Your kit is a good start, there's always more you could add - PLB, Flares (or other signalling device), aqua pack for your phone, fixed VHF etc etc. another option is to go out in company, plenty of guys around Dunbar and North Berwick with Ribs.