Monty has a favourite toy—his yeowww catnip banana. The catnip in this is very potent, as we first bought the toy in 2015 but it still gives him a catnip high! Monty would first lick the catnip banana, then he would bunny kick it with his legs. That's how he gets catnip high.
Harriet also has a yeowww catnip rainbow which she adores. She'll toss hers around.
Max is the only one among the three who is immune to the pleasures of catnip. I've tried various catnip toys on him but the result is the same. He just doesn't find catnip attractive. He belongs to that small percentage of cats who do not respond to catnip.
I learnt that the best way to store your catnip toys is to keep them in a Ziploc bag after each catnip session. This helps to keep the toys' catnip smell intense and concentrated for a long time. You could even toss in other toys in the same Ziploc, sort of like marinating them in catnip scent.