(Coming from: someone who reads CVs/applications frequently as part of my job, in contexts where it is routine for applicants to be highly intelligent people with high achievement.)
For both MENSA and DYS: I wouldn't recommend listing them, if all the applicant did was to be a member, use the organisation for socialising, use it to give support to parents, etc. Rationale: by college age, high ability ought to be evidenced by the student's achievement. If it is, you don't need these stamps of approval. If it isn't, high IQ isn't actually a plus at all - it just raises red flags as to why this high potential individual isn't achieving their potential.
(By contrast, as a parent filling in a selective school application for a child up to early teens, I would certainly use these things.)
If the applicant has actually done something with the membership - has started and run a special interest group, say - then by all means list it, but emphasise the activity not the exclusive parent organisation.
One might argue that it's sensible to list these things even if they won't help much, on the basis that they won't do any harm. IME the stereotype of people who belong to high IQ organisations is prevalent enough that this is risky. No recruiter is going to act on the basis of that stereotype consciously, of course, but you are wise to avoid setting off unconscious biases against you, too!
