Hi Malc, welcome to the world of ribbing. The list of what you should have is non exhaustive. Obviously you'll appreciate the need of life saving equipment. However, a well maintained boat, engine and skippers interlect will always stand you in good stead.
Anyway, I woldn't leave port without the following.
Life Jackets sized appropriately for you and your family.
An anchor with plenty of chain and warp.
A sharp knife (rope around the prop freed with the same or the RNLI for the lack of)!
A reasonable appreciation for the "rules of the road" which will keep you out of getting into trouble in the first place.
A chart of your chossen cruising ground and a basic idea of how to read it along with a tide table.
A vhf (with or without licences).
A GPS (handheld or fixed).
The latter (GPS) is not crucial especially if you're a beginner and only hopping from place to place amongst the many who do the same each weekend, however, you do need one.
A VHF should however be high on your list of purchases especially when cruising around this time of year when there are fewer and fewer vessels about who will respond to the "waving arm distress call".
Basically, it's about enjoying yourself whilst feeling secure that if something goes wrong, you're able to safely get yourself and crew back to shore.
Use your common sence. Tell someone where you are going and what time to expect you back. With a VHF you can advise H.M.C.G of the same.
If you get into trouble you can drop the hook, use your chart to tell people where you are, your VHF/mobile to call other ships / shore / CG. Flares to be spotted if needed. Tow rope for the pull home and life jackets in case of the worse.
As for an AUX engine.....well, that's a good question which with time you should be able to answer yourself.
My best advice would be to get together with other like minded enthusiasts, bum a day out in their boat and learn a few things that way.
You're always welcome aboard mine.
oopps - Compass