I'm doing ROP format ladders of push ups and explosive rows with double 24 kg when I can (seldom), and in the week-ends when I don't do S&S, I'm testing a snatch routine I tried to design because I'm a fool and think I can design programs and because I can't stand to swing the 32 kg everyday wtiht a sustainable effort but not being able to snatch the 24 kg to save my life! I still think it's not the best choice to mix S&S with anything else before at least having reached two sets of swings and get ups with the 32 kg. I know it can take months and doing just two exercises over and over again can be boring after a while, but if, like me, one starts from the very bottom of the fitness level and works his way up to full 24 kg S&S, the protocol demands absolute concentration not because it's particulary hard, but because a certain level of proficiency it's needed before adding things to two movements that are, in my opinion, some of the best for the health of the body if done correctly, but can easily and quickly become dangerous if "taken lightly".
I don't take varity days, but if I did, I'd probably do some bodyweight work just because I happen to like it and to a level that will not interfer with S&S.
OS resets, Yoga, Martial Arts form practicing and drills, shadow boxing or heavy bag interval training for three minutes rounds I think would be awesome choices too to had mobility and a different type of stimulus (especially kata, shadow boxing and the heavy bag).
You can also finish S&S sessions with some specific grip work in which Mister
@Geoff Chafe is expert, which I think is always a good idea and an important aspect of strength training.
Choices are many!