My ds is 3.5 years and is grazer. Snacks have become the main flashpoint for tantrums. He also has a new sibling and constantly asks for food (despite good mealtimes). This is really tricky when feeding a newborn.
He has taken to using his step to get snacks. So today I have set up a low level snack cupboard with only healthy snacks - rice cakes, fruit etc... and little bowls to put them in. When starts his whining I showed him and explained it is his cupboard to prep his own snacks. I thought by giving him responsibility and trust it might prevent problems.
Those who say their child only has two snacks a day - for this little boy that would not realistically work.
Yes my little girl has phases of 'grazing' and is small, so we sometimes do this (we have been advised she should have access to food whenever she wants as she's light/little. However when I say grazer she also eats meals too! Weird kid prefers lean foods and hates fat/sweet things).
Be wary of too much fruit - bad for teeth, filling and not many calories. For the same reason I prefer oat cakes to rice cakes (also a new baby cracker called 'yummies' with spinach in. DD's favourite pudding. Not a stealth boast, I'd love her to wolf down cake and gain a few percentiles!). I also put in dry low/no sugar cereals in little bowls, raisins, dry toast, fresh berries (I cut grapes obvs) etc and put them out like a little buffet on a low table.