In order to avoid having to waste food, for me, I serve only as much as I can eat.
I don't want to leave any food on my plate, so I only take as much as I know that I can eat.
ご質問ありがとうございます。
①
"In order to avoid having to waste food"＝「食べ物を無駄にしなくて済むように」
"for me, I serve only as much as I can eat."＝「私が食べられる分しか自分によそいません。」
②
"I don't want to leave any food on my plate"＝「自分のお皿に食べ物を残したくないので」
"so I only take as much as I know that I can eat."＝「自分が食べられる分しか取りません。」
ご参考に！
"Serve yourself only as much food as you can eat." 「自分が食べられる量だけ食べ物をよそう」 というフレーズが使えます。
他にも以下のような表現があります：
"Take only what you can finish." 「食べきれる分だけ取る」
"Portion your food to avoid waste." 「無駄を防ぐために食べ物を分ける」
"Dish out only what you can consume." 「消費できる分だけ盛り付ける」
アメリカ合衆国 
