He should study something that he is truly interested in as an undergraduate to optimize his GPA (attitude = 99%). The major tests for admission to grad schools can all be studied for when that time comes. Having the ability to reason and calculate (college calculus will be more than enough) and have a good vocabulary will be all that is necessary coming out of his undergraduate years to be ready to take the tests.
I agree with staying away from degrees that go stale quickly like CS unless that is his genuine hobby interest (you can keep current outside of the office).
Business degrees like accounting work fine for many graduate degrees and can be quite valuable in the military.
Seeing though that he is rather undecided, he needs to design a schedule of courses that allows him to explore possible candidates early on so in the event of a change of heart (very likely) he can change to something more desireable using the other credits to satisfy General Ed requirements.
Let's say he is not totally turned off by these 3 areas:
Life Sciences
Business
Political Science
For Life Sciences and Business Majors, Calculus will be required, more with Life Sciences, some with Business, and perhaps a single "quantitative reasoning" class in the gen ed requirement for the liberal arts. Calculus is a prerequisite for many Life Science types courses, so it should be taken 1st term.
Economics will definitely be required for Business and probably for Poli Sci and all Science Majors will need some social science credits in the general ed department. It may be required for other business courses (many require more econ for upper division work depending upon the emphasis).
A basic Poli Sci class will probably not be required for Business or Life Sciences, so you might not put as high of a priority on it. Plus most liberal arts type degrees don't have long chains of pre-requisites, so if you get a late start on it, it won't pose a threat to graduating in 4 years.
The point of this discussion here is that your son should evaluate ALL reasonably likely majors and start out with classes oriented towards those with the longest chain of pre-reqs in his first term and fall back to other majors with shorter chains later.
So for those 3 interests above, a 1st term schedule might look like:
Calculus for math/science majors (will satisfy all major requirements)
Biology for Life Science Majors (not the one for liberal arts majors)
Economics (Generally this is a one size fits all)
Chemistry (for science majors)
Poli Sci (the core class for the major)
In the first term, this student should figure out:
1) Does s/he have the chops for math/science at this level (many don't)?
2) Can s/he write well about theoretical ideas such as political theories (some figure out that writing papers isn't their thing)?
3) Do the theories of money and related issues of finance strike a level of interest?
I put both bio and chem in the first term because they tend to have long pre-req chains. The calc is probably required for both of them as well. Note that English composition is missing. Hopefully, his/her writing skills will be sharp enough without it to survive an intro social science class.
With this schedule, the student should be able to eliminate at least one of the 3 areas of exploration, perhaps 2.
Second semester could be done as follows if s/he cannot decide between 2 areas:
Life Sciences/Business
Calc 2
Bio 2
Chem 2
Accounting
English Composition
Life Science Poli Sci
Calc 2
Bio 2
Chem 2
English Comp
Other Poli Sci Core class (Sociology?)
Business/Poli Sci
Calc 2 (if required)
Accounting Core Class
English Composition
Statisitics (if required for Poli Sci - always required for business)
Core Social Science (like Sociology) for Poli Sci majors
The concept here is that as you eliminate areas, keep taking core classes in the major area and secondary classes that are required for both areas still under consideration.
Bottom line is for the undecided major who has to gradutate in 4 years to explore majors based upon keeping the most options open the longest. It may not be optimal for the GPA as weaknesses may be exposed, but this minimizes any possibility of second guessing later on.
Oh and he should get used to filling out 104R's on a regular basis