would it be ok to use a schoolbag and place weights within it to replicate a weighted vest as i dont have one? could this cause any potential injuries or strain on my body?

right now i could do about 24 chin ups and about 13 pull ups, so how much weight would you recommend without weights? and how many reps should i be aiming for?

also could i use the schoolbag with weights for press ups?

much appreciated guys, thx!

24 chin ups and 13 pull up?? they are both the same thing right? Anyway once you get over 15 clean chin ups with your bodyweigght, its time to add some resistance, like your bag with weight should be fine. Anywhere between 8 and 15 for chin ups should be fine. It really depends on what your goals are...build muscles?? muscle endurance??
Or just toning (which you do not need extra weight)

why don't you try varying the grip (i.e. width, overhand/underhand) and see if you can still do as many?