Two follow up questions (unrelated to each other):
1) How do Pokemon without arms “hold” items”? I realize it would vary (and I’m not asking you to explain ALL of them) but just… like how do you give voltorb a quick claw? And even ones with arms, how do they battle without being severely handicapped from having to hold a berry without crushing or dropping it in a huge fight?
2) How does Pay Day work then? I’ve still never understood where the coins come from.
1) We do see quite a few Pokémon in the anime holding one particular type of item: Mega Stones. The stones are usually set in wearable accessories – even for Pokémon with dextrous hands, like Lucario and Gardevoir, so as not to interfere with battle techniques. You could probably generalise that to most other items, and create custom fittings to suit the anatomy of almost any Pokémon (Voltorb is admittedly a difficult one, but I’m willing to trust that some Poké-world artisan has figured it out). I suspect trainers may be able to buy an assortment of these from specialty tailors and jewellers.
2) I would really love if it were something akin to the Harry Potter series’ “leprechaun gold” – if the coins were magical illusions that vanish after a few hours, so that we’ve all been cheating shopkeepers throughout the Pokémon world for decades. But you’d think they would have figured out some way to check, and obviously in the games we can keep money generated by Pay Day indefinitely without it disappearing. So probably the answer is just that Meowth like to collect round or shiny things, especially coins, and keep large stashes of them (maybe in… pouches, making Meowth actually a marsupial?), but will hurl them at enemies to attack if necessary. There is a reason Meowth have the Pickup ability, after all; they collect things without necessarily being ordered to. Perhaps the charm on Meowth’s forehead is magical, and allows it to sense valuable objects to collect; maybe it even acts as a sort of Purse of Holding and can store large numbers of coins or other small valuable tokens.