What do you need a portable potty for? That wasn't even brought up in the show, so why do you need it in the game? And don't give me the "it's got to be realistic" crap. And just what is the story? Does it follow the first 50 episodes of Season 1 or is it something else?
Or instead of collecting floppy discs for your Digimon, why couldn't you have something similar to the Ben 10 game alien switching? The Omnitrix's power gets depleted as you stay in alien form and then recharges when you become human again. You could have the same thing; use up too much of Tentomon's Super Shocker and he reverts to his younger self. And as you level up, the amount of energy grows as well. Or more technically, as you and your Digimon grow closer. Hmm, but I guess they're there for the same reason that there're tonics and ethers in Chrono Trigger.