I either have everything on the bike (pump, tubes, repair kit, tools) plus pockets for snack,key, phone, waterproof, or if I’m touring overnight / commuting / need a big camera , have a really big (fits a 13″ laptop) saddlebag.
I’ve done lots of miles with and without rucksacks, and it is just more comfy not to have one for long rides, particularly if like me, you sweat a lot.
If it is just a pootle for the sake of riding, it is easy enough to do a hundred miles in comfort without any need for extra bags – I think I stopped once for food last one, but only cos I was bored of soreen.