Cooking for lots of people has always been a challenge . I hope this will help you to make better decisions when preparing your ingredients .
Standard servings .
3 to 4 oz of proteins
4 oz starch
4 oz vegetables
2 oz bread
2 oz to 4 oz dessert
10 lb meat serve 40 people
10 lb vegetable same
Pasta, rice and most of dry beans double their size when cooked . One cup of dry rice serve 4 people,cooked rice
Consider half medium potato raw for one person by cooking and adding stuff making mashed potato or just plain potatoes. Bake potato consider one per person.
If you open can products folow can instructions.
Dinner rolls or sliced bread should be preporteioned for 2 oz .preslice deserts for same amounts .
Modifying the number and the oz should help you now cook enough for everyone
Smart Food Solutions 
Love these posts- such great info!
Thank you