Good list but a few other points:
No need to file a flight plan two days in advance. Leave it till you are certain you are going!
No GAR required on the way out (unless you are going to Ireland, Isle of Man etc)..
You also need to notify Customs/Police at the French airfield you intend to land at first, sometimes over 24 hours in advance. The main ones near the short hop over the channel are Calais, Le Touquet, Merville and Albert-Bray. However, sadly, not longer Abbeville.
Almost no point in a life jacket unless you also carry a survival suit (and life raft if you have the space). No point is being kept afloat till you freeze to death!
Suggest you also take a PLB (and possibly handheld transceiver).
Finally, if you can, go with someone else who has done it before or in loose formation with another aircraft.
Martin Ferid of the LAA has organised several trips across the Channel recently,including one to Amiens last weekend (via Albert-Bray, I think). He has also written several informative articles in the LAA magazine about potential trips. Well worth a read.
PS You are also supposed to carry the aircraft documents (permit to fly etc)and your licence. I prefer to carry copies of the former.