Hope it went well!
Like @Bbt67 says, your FTP determines how many calories you will burn. If you go to the Reinstein workout page it’ll tell you your figure. For me at 270 FTP it’s 1,062 - but it could be a lot higher or lower for you.
My approach - based on Amber Malika’s advice on the TR AACC podcast - is to match the calories consumed before, during, and just after the ride with the calories burned.
Then the intensity of the ride will determine whether I make it high carb, medium carb, or low carb (as well as determining the timings of the food intake).
So if I was doing Reinstein (which has some fairly intense over/under intervals) on a weekend morning, I would match the 1,062 calories burned with something like:
80g oats (dry weight), 35g sultanas, 25g scoop peanut butter, 10g honey (2+ hours before)
1 banana (1 hour before)
2x bottles made with 50g energy drink mix each (during)
If I was doing a lower intensity session like Baxter I’d be more likely to cut the sugars and match the calories with a higher proportion of protein and fats, e.g. just have sugar-free squash instead of the energy drink mix, use more peanut butter, substitute some of the oats for scoops of greek yoghurt, have a protein bar, etc. I might even do an easy session fasted and then replace all the calories after the ride.
This is the spreadsheet I created to figure it out. It’s locked for editing but if you do “File > Make A Copy”, you can make your own version and personalise it. Feel free to PM me if you want instructions.