Thanks for sharing your recent experience climbing Mt. Rainier! I think it’s worth considering focusing more on heavy carries to improve your strength and endurance. Additionally, you might consider the lack of acclimatization that you had on this trip. I think it would be helpful to spend more time at high altitudes before attempting a summit.
In terms of fueling, I know freeze-dried backpacker meals are a great way to ensure you’re getting enough calories while on the trail.
You can also check out https://traveltweaks.com/how-to-plan-a-trip-for-the-great-migration-safari-in-tanzania-36330/ for some tips on how to plan a trip and improve your chances of success.