Galen Wilkerson wrote:
I'm interested in figuring out what the best gear would be for a
kayaking trip like this:

Fly to france, paddle on canals/rivers (not whitewater) and down to
the mediterranean, then bounce along the coast or out to islands in
the med. etc.

I'm looking into a folbot with sail kit, but of course wonder if the
mast can made to fold and also be brought as luggage, etc. etc.

Folbot and other manufacturers make sailrigs for their boats and you can
also buy such rigs from Balogh and others. The sailrigs fold up into
packages of various sizes - I believe Folbot's current upwind sailrig goes
into a bag that's about 4' x 1' x 0.5'. Simpler sailrigs are available if
you only need to sail downwind (and paddle when needing to go upwind).
Even a large golf or beach umbrella can work well as a downwind sail.

I
wouldn't want to have to paddle across large open bodies of water.

Be sure you know what you're doing before sailing across large open bodies
of water. Kayaks don't make particularly good sailboats so progress will
be pretty slow and give storms plenty of time to develop. Many of the
sailrigs (incl. Folbot's) come with outriggers for added stability but a
storm will put lots of stress on rather lightweight parts. The outriggers
provide stability against short gusts of wind that might otherwise
capsize you but aren't intended to work that well in large breaking seas in
the open ocean. You'd better be prepared to first reef the sail and then
take it down completely if the winds grow too strong.

Also, it might be nice to be able to portage, so some kind of wheel
kit could be useful, and I would probably bring a large daypack for
hiking excursions, etc. etc.

A cart is definitely useful if you need to transport the boat/sail/gear any
distance. If possible get or make one that can be used for either the
assembled boat or the bags. Some of the better quality folding luggage
carts might be adapted to also work with the assembled boat but usually
don't handle rough ground well due to small wheels. Regular canoe/kayak
carts are better for that type of surface but are awkward for carrying the
boat/sail in its bags.