I have almost always been asked to show a passport on the 4 or so trips I've done to Alderney... (not been for about 5 years though)
Plus, there is (or was) a mandatory requirement to wear a 'Q', (yellow) flag on entry into Alderney.
Double Plus, the Channel Islands are not part of the UK or the EU, and thus, since you are leaving and on return, re-entering the EU, your vessel becomes subject to customs requirements, (though not Immigration ones). That means you need to inform Customs on your return to the UK and the way I read it, it would be advisable to fill in a C1331 form before you leave.
I know most people ignore this and will tell you otherwise….. and I’ve only heard rumours of one case of a fine, travelling from the Channel Islands and entering the EU in France without notifying…. But if you want peace of mind, see here.
If you go straight to France, you just need the stuff Doug said.
I would stongly recomend getting the SSR!