Any science degree will likely do. Pick something you might consider doing in the event you do not get into medschool or change your mind later. It is VERY competitive and most are not accepted.
You will need a fair amont of Bio
Year chem
Year organic Chem
year physics
MCATS are the first cut because it will be the only thing you have in common. It is very improtant to do well.
You will need good grades and unless you have a 3.5 or better it will be harder to get in. Less than 3.0 and you can pretty much forget it.
References
Interviews
Things would make medschool easier when you get there:
Anatomy and physiology
Cell Bio
Microbiology
Biochem
Pharm
It really is not that the material is all the tough to understand, once you are to that point of course, it is the sheer volume of it. About 4 times the pace of undergrad.
Your 3rd and 4th years of medschool are a degrading, shit swallowing, experience you cannot prepare yourself for. I would go thru Marine Corps bootcamp a dozen times before I would subject myself to that again.
Residency is even more work but a little less shit swallowing.
I doubt it is really what you think it is but I tell everyone that. I worked at Mayo before going to medschool and there were plenty of docs to ask. Only one told me he would do it again. Guess which one I listened to?
Good luck bro, you're going to need it.