In terms of course selection, if you want to minor in religious studies, check this out
http://registrar.mcmaster.ca /calen...nt/pg1740.html
You can complete your minor with the "electives" credits that you have to take in your 4 years.
If you want to do a double major then I won't be able to help you with that 'cause I'm doing a major and minor as well so that's what I'm aware of but check the calender.
And as for the courses that are full, unfortunately, that's tough luck 'cause the SOLAR has been opened for a while and core courses go fast especially first year ones, nevertheless, keep checking SOLAR to see if it comes available and keep checking the "official course trading thread" on here to see if people are dropping it. Otherwise you could try taking mainly your religious studies courses this year and register on time for life science courses in the summer or next fall
Hope that was a bit of help!