Kind of depends on what you are looking for benefit wise (obviously an extreme endurance event like this is different than bodybuilding but it is still "broad").
I don't have much drug knowledge so I'll default to other valuable members there.
Again it will be dependent a bit on your situation and how you approach your training, but here are just a few things that come to mind:
1) I love the carb and electrolyte recommendations above. This is huge. Individual tolerance to amounts on types of carbs can be a bigger issue in this situation so don't be afraid to try a few combinations. In general you want a mix of carbs (in short varying sources will allow for better utilization/uptake with less distress). I'd say give the Cytocarb a shot, maybe try some different mixes (dextrose, HBCD, Carb10, etc.) to see how you react, and maybe something like Morphogen Hexagen (Glycerol and Creatine have some research for these kinds of things and regulating body temp in longer strenuous events, but it will depend on if you don't mind the possible extra weight they may add to you and it has lots of other electrolytes, Ornitine, and Actigin that may help performance).
2) Adaptogens! There are tons of options here, but with the stress of training amounts these could be really helpful. Something like Peako2 that has a solid blend could be a good option (that I love). Or individual strains of mushrooms, things like Ashwagandha, Rhodiola, etc.
3) I know you asked for performance but I'd keep in mind maybe supplementing something for joints as a preventative before anything gives you trouble. UC-II, Cissus (I like SNS Cissus XT), Boswellia, Curcumin, etc. Morphogen Orthogen is loaded if you want a shotgun approach.
4) I am also a big fan of Robuvit. It has some cool chronic fatigue benefits, but has also been shown to improve endurance for tri-athletes:
https://pubmed.ncbi.nlm.nih.gov/26488613/
Good luck and hopefully that gets you started on some possible options along with the other things mentioned already.