Maybe he just doesn't want so much junk food? I would try giving him a choice between a couple healthy snacks. Include peanut butter or yogurt for dipping, try and make it fun. You could have him help by making something fun like bagel pizzas--bagels, spaghetti sauce, cheese, toppings then bake at 350.
Here is a list of healthy snacks or meal ideas, you might be surprised what he'll like.
All veggies cut up (bell peppers, carrots, tomatoes, etc)
Almonds
Apple chunks
Apple pieces
Apples
Avacado chunks
Avocado slices
Baby spinach leaves
Baked apples
Banana chunks
Banana pieces rolled in oatmeal
Beans
Berries
Black bean patties (homemade)
Blue corn chips
Blueberries
Boiled peanuts
Canned green beans
Cantaloupe
Carrot sticks
Carrot strips and frozen peas
Cashews
Celery sticks
Cereal with raisins mixed in
Cheerios
Cheese cubes
Cherry tomatoes
Cooked pasta (in different shapes, my DS loves eating cold cooked rotini)
Cooked yucca chunks
Crackers
Croutons (homemade)
Cucumber slices
Cucumbers
Dates
Diced lunchmeat
Dried apple rings
Dried apricots
Dried cranberries
Dried fruit (w/out the sugar and chemicals)
Dried papaya
Edamame (cooked & shelled)
Figs
Fish Crackers
Fresh apple
Fresh peas
Frozen blueberries
Frozen peas
Frozen veggies (yep, still frozen!)
Fruit
Fruit leathers
Fruity booty, veggie bootie, pirate's booty
Garbanzo Beans, roasted or boiled
Goat cheddar cheese
Goat chevre
Graham cracker sticks
Grapefruit
Grapes
Hard boiled eggs pieces
Healthy mini muffins
Homemade fruit pops
Homemade granola
Honeydew
Hummus
Hummus and rice crackers
Kidney beans
Kiwi
Korean Pear cut-up
Leftover pizza
Little beef jerky bits (depending on # of teeth and age of child, of course)
Mango (dried or fresh)
Meat or "meat" roll-ups
Mini cashew butter sandwiches
Miso
Nori (strips to chew on)
Nut butters
Nutbutter balls (rolled with pretty much whatever your child likes)
Nuts
Olives (limited though, since so salty)
Orange sections
Organic cereals
Organic dried fruits
Pancakes or waffle sticks
Peanut butter or almond butter
Pear slices dipped in fruity yogurt
Peas
Pieces of Swiss cheese
Pineapple
Pita wedges
Popcorn
Prunes (not too many)
Puffed rice/millet (or kamut/wheat)
Pumpkin seeds (shelled)
Raisins
Red seedless Grapes
Red/yellow/green pepper strips or rings
Rice cakes
Rye crisp
Seasoned & baked sweet potato fries
Seed mixes
Shredded cheese
Sliced Nectarine
Sliced plum
Smoothies
Snap peas
Sprouted almonds (peeled)
Steamed broccolli
String cheese
Stuffed grape leaves
Sunflower seeds
Sushi rolls
Sweet Potato (cut into chunks, toss in oil, roast)
Toast tortillas
Toasted English muffins
Tofu- Cubes
Tomato chunks
Trail mix
Unsalted prezetels
Unsweetened carob chips
Various dried cereals
Whole grain cereals (mostly for baby to snack on)
Whole grain crackers
Wild rice sesame sticks
Yogurt