Rare mushrooms add 50 food per. Don't decay. Easy to get from megachelons. Rare flower work as well. Beware they starve extremely fast. So only food with high enough food value will keep them alive. Aka not the seeds u get from megachelons. That will cause them to starve faster than they can eat.
When raising baby gachas, don’t put food into their inventory. Drop stacks of berries in front of them. The difference will be 5 berries as opposed to their weight being full so for eg 5k berries instead. And they do consume food fast. Also putting them in kangaroo pouch of mate boosted pair helps to slow consumption rate I believe.