Lots of wisdom here (on the liquid thing). In fact, what you describe is what I actually DID for my last brevet series and it worked great.

I haven't done anything over 200 miles since 2011, and sort of got in my stubborn head recently that maybe I could do it all on real food. But having one of my bottles with sustained energy in it always worked really well for me. I don't generally do gels or other stuff, but I would start with 2 bottles of SE and then keep one of them with SE or something. In the last half of a 400 or 600k, I could never really tolerate the liquid stuff, but I felt like at least I'd pre-loaded with calories pretty well by that point.

Thanks for reminding me. Now to see if my bins of sustained energy have expired.