The most important things is your medical certificate. Always have this around with you and use it to get excuses. The sergeants will mostly likely not force you to over exert yourself.
Don't worry about the training, it is not intense. In fact, they deem running, pull up, pumping as a dangerous activity for PES C. You will rarely be asked to run, mostly power walking. You will still go through live grenade throw, SAR21 firing, urban ops, buddy aid, one activities which i forgot the name and 2D1N field camp. Be prepared for muscle soreness after carrying your wife for the first day.
The most strenuous activities is a 2D1N field camp. Carrying 30kg load without condition will kill your back. You are also required to pitch a tent with your buddy within 15 minutes in SBO and your wife(Total of 10kg load) under hot sun.
Depend on your company, " knock it down" as a punishment are not allowed for PES C.
Overall, quite slack. Quite hectic schedule, everything is cramped into 4 months of Tekong BMT and then you will be posted out for vocational BMT.