Sounds like you are one month away from starting a trip that most people are saying you should not do, or that you should find a different location instead. I won't pile on too.
Choice of bike - I looked up Ridgeback and they list three touring bikes. All three have triple cranks and what looks like an adequate drivetrain. Two of the three were listed as steel frame, I am not sure on the third. The best bike is the bike that fits, if your bike fits you well and you know it works well, bring yours and do not roll the dice on a different bike.
You can have a bike shop pack your bike, find a bike shop in California to re-assemble it. Pick one before you travel in California so that they can advise you on any extra details you may need to know.
I am not familiar with British Air luggage policies, but if you use Delta, United or American Airlines, these airlines canceled their oversize fees for bicycles a few years ago and to the best of my knowledge you can bring a bike over in a bike box without an oversize surcharge with those airlines. Other airlines probably have extra fees for a bike. But before you buy a ticket, look at their luggage policies to make sure that there are no nasty surprises.
Panniers, you should be able to buy some good ones in UK, make sure that they fit your racks. Ortlieb are very popular panniers. In UK, Carradry are also a good brand. I have used both Ortlieb and Carradry, happy with both. I however did find that Carradry did not fit my rear rack well, that is a good reason to make sure everything fits the way it needs to before you leave home. I fabricated a different set of lower hooks for my Carradry to fit my rear rack.
You did not say enough about your plans for me to elaborate in more detail, are you planning on camping or staying indoors, etc.
In UK, you have a national health care plan, here I have no clue what your plan covers, if anything. That is something to research.
Last edited by Tourist in MSN; 05-11-23 at 04:08 PM.