I think it's useless to reinvent hot water here. Sandwiches are the law.
I don't recommend gel for the mountains, unless in the last 45 min you go into "filter". Better energy bars if you insist.
White bun and prosciutto or banana is the law. If it satisfies TDF cyclists, it will satisfy you too
P.s.: Gel is always at the end, never in the middle of a long effort. More harm than benefit.