Sorry, don't have a list but I can remember a few things..
You have to register for the compulsory Chemistry units, worth 2.5 units in total (0.5 units each for Basic Physical, Organic and Inorganic modules, and 1 unit for the first module 'Introduction to Chemical Principles) - there weren't optional chemistry units.
Those who didn't take maths have to take Quantitative Chemistry (basically maths) which is 1 whole unit.
If you did take maths, then I think you are encouraged or expected to take a maths unit within the maths dept. I'm unsure if that's worth 0.5 or 1 unit. (I *think* 1 unit).
You can take up to 4 units for year 1, so most people have only a half unit to spare.
I would have taken Cellular and Molecular Biology, but it was worth 1 whole unit!
You can choose Human Physiology or Mammalian Physiology.
Geology.
There might have been something Psychology related, business/management (don't quote me on these ones but I vaguely remember it), I think Archaeology...definitely one involving statistics (may've been statistical computing, but again..can't recall fully)
Basically, they give you a list of options that can fit in with the chemistry timetable (and telling you what times/days the lectures are) and you'll more than likely end up doing it by a process of elimination by your interests and how many units you have to spare.