I’ve found that bamboo plus carbon fiber and epoxy (or Titebond III if on a budget) with spray foam sprayed in the core, makes for a very strong and tough structure. Note, you have to sand down the bamboo’s outer coating a bit first, since the first layer(s) are so silica rich and not as easy to bond to.
Since carbon fiber is on the pricey side–there are a couple alternative options that in combo make for something just as good, but less expensive.
S glass fiberglass plus carbonized cellulose nanocrystals. The latter can be made at home. If you start with a source that already contains a high percentage of CNC (hint, most of the bast plants used for fiber), then you can get pretty high levels if you do the chemistry, timing, and temps right. A little C-CNC goes a long way. Some of the research literature I’ve seen references to 2% C-CNC to epoxy by weight for the ideal increase of different strengths (mainly tenacity and stiffness).
S glass fiberglass’s specific strengths (strength to weight ratio) are only slightly below that of carbon fiber, but it’s much cheaper. Even better, you can do a loose wrap with carbon fiber tow first (much less expensive than the cloth, and then overlay with the S-glass plus C-CNC in the epoxy, then use spray foam for the core. Would make for a ridiculously tough and strong structure.
(as to why I started experimenting with the above combo’s–I was interested in cutting up a steel mountain bike to make it lighter, and adding composites into the frame)