Was racing for 7hrs this summer. Usually 2 feeds with fruit & water but no energy bars/drink.
I used camelbak but would like the option to go without.
I can fit a bottle on seat post, but not with a saddle bag (if much lower than in the attached picture it interferes with the rear suspension).
This summer I was carrying**: tube, levers, gas, mini-tool, tyre boot, whistle, phone, survival blanket, mech hanger, gels, energy powder, gilet. Too much for pockets.
Think top tube storage combined with pockets is probably the solution.
[** race requirements]