I too use a Maxped bottle holder to hold my nalgene, cup, and other items. To increase the space, I trimmed out the insulation and inner layer of fabric. I now can squeeze in a Trangia burner and a fuel container.
Thanks, I should have also mentioned that. I carefully cut out the insulation, too. That made enough room that I can fit a bain marie pot in there. That's an insert made for commercial steam table/wells in a restaurant. They're heavy gauge SS and have a lid, and I found a 1 L one that nests nicely with my 40 oz bottle. Not as light as a $50 titanium pot much it only cost about $4 with lid at a restaurant supply store.
Thanks to to the OP for the original post. I don't mean to hijack it; it's a very good idea. Your first post gave me a few ideas to tweak my own kit. I should take a few pics of the contents of mine. Mine is also biased heavily towards fire.
Using the bottle holder does as some bulk but it also provides a means of carry. It has a should strap, plus it has a bunch of MOLLE webbing to either mount it to a pack or lash it to a vehicle. Lots of options.
At any rate, I personally don't like to carry an empty water bottle. You save the weight of the water but none of the space; plus, I would rather have the water! Of course if I lived in MN instead of SD I probably wouldn't carry water, just the container. It all depends on your environment.