On 10-day Euro-tours I only take old=style running shoes (
hi tec silver shadow) and toe clips.
On my first big tour I also took some Teva sandals. My feet really appreciated the change in footwear and they did toughen my feet up a lot. Towards the end of the tour in Sept in Norway my feet were wet for many days and I got a really painful trenchfoot type conditions. Sandals were the best footwear to use off-bike even in colder conditions.
Some form of alt footwear is useful and a flip flop is fine if you like that style.
Some
ultralight DIY flipflops.