My toddler sons are the same. It is difficult, They will eat half a banana, not like a soft spot, throw it away and get another. We can go through 2 bunches in just a day, same with apples, bread, yogurt... pretty much anything! So, we definitely feel the economic crunch seeing our food get trashed and running out by the end of the week.
We have to lock our fridge and pantry otherwise it would be empty in a day.
When they beg for snacks, I find it is often out of boredom, so I try and redirect them with an activity, go to the park and go home.
Also, let him know his snack schedule, so he will know when the next one is coming. Have a predictable time frame, so he knows, after this specific cartoon and color time, will be snack time.
It takes a while, and is easier said then done, but it helps. Also, he could just be going through a growth spurt and his appetite may calm in a while.
Oh, just wait till he's a teenager, ha ha!!