How do you resolve issues with kids wasting food?

If mine ask for it they have to eat it.
If they refused to eat it they would not get a substitute.

I told her point blank, either you are going to eat it, or you aren't.. If you aren't going to eat it, I'm not going to give it to you ANYMORE.. NONE.. and nothing to eat until, the next meal

Would 2 1/2 be too young to implement that on? Just curious.

No substitutes.
Don't get mad, don't sigh, don't angrily throw it in the trash.

Have set meal times and snack times.
Do not let your kid wander and play while eating. He can have a cup of water while he plays but milk and juice are served only at meal times and only at the table.
If your child doesn't want to eat what you offer (even if he asked for it), tell him, "That's fine. But please stay here and keep me company while I eat." He may very well eat it after a few mintues.
If he does eat, great. But don't make any comments.
If he doesn't eat, oh well. Don't make any comments.
If he comes to you minutes after the meal ends and says he's hungry and wants a cookie, tell him "No. You can have a snack at snack time." and calmly walk away.

You are responsible for when food is offered and what is offered.
Your child is responsible for what he eats and how much.

I wrap it up, put it in the fridge, and tell them when they get hungry- that is what they get.

And no- 2 1/2 is not too young- if you cater to her now- she will learn to expect it...

And no, 2.5 years is plenty old enough to go to bed hungry if that's what he chooses. He will test you to see if you mean it. Stick to it. Calmly and quietly.

This is also the age when he needs to learn table manners. At this point that means:
No screaming about things he doesn't like. Teach him to say "No thank you".
Staying with you for a reasonable length of time to "keep you company". Meals are very social and he will learn what to eat by watching you... even if it's years before he's willing to try it.
He may make a mess, use his fingers, etc. That's OK. He'll more "table manner" things over the years.

I give VERY small servings and insist they eat most of it. No substitutions. They can have seconds if they want more. I try to have side dishes they like.

I never insist that they eat anything, but I will not give a substitution for my 2 year old. If she changes her mind, I would never force her to eat it.

I just make somthing else..Its really not like im going out of my way or anything.I just want my child to eat and will not let her go to bed hungery because I have done so before..was not the best Idea for us lol.I always keep somthing quick and handy in the freezer just in case she wont touch dinner.

Eat it or don't eat. My oldest did this. She would beg for something, take one bite, then say she was done. I just serve it over & over again. Nothing else until it is gone.