every little bit will help.
depending on your exercise routine your diet will need to vary considerably.
try making one change to your diet a week. this way you will get used to eating healthy.
adding specific items to your parents grocery list should be easy to sell to them
try doing something like this:
week 1: cut out all regular sodas and non 100% juices
week 2: eat a healthy breakfast every day. try oatmeal with splenda or other sugar free sweeteners
week 3: make a healthy lunch and snack for yourself every day. If you are eating at 8:00am 10:00am and at noon, you will not be as hungry for the rest of the day, your metabolism will be working properly, and you will be a lot less likely to binge at dinner.
week 4: add another meal between lunch and dinner

other tips: look up the nutritional information of common places you eat at online. look through the menu and find healthier choices if you go with your friends.

if you work these tips into your diet gradually, you be much better prepared for a body building diet if you gather the will-power it takes to stay on one.