Dear MBApplicant,
It depends on why you are building an alternative transcript. If you are trying to demonstrate quantitative aptitude, then you should take math courses (college algebra, finite math, calculus). If you are trying to demonstrate you can succeed in the classroom and you scored well on the quant section of the GMAT, then you could take some business courses and/or math courses. Which business courses you take are up to you, but most folks tend to take either finance, accounting, or statistics.
Good luck,
Lisa