I want to order as much as can fit in one container.
I want to order 1 container's amount.
ご質問ありがとうございます。
「詰め込める」はpackとput inと言えますので、as much as can be packed inに訳せますが、as much as can fit inがより簡単に言えると思って、提案しています。
回答の英文に商品を入れることができます。
例:I want to order as much wine as can fit in one container. (数えられるものなら、as much asじゃなくてas many asになります。例:I want to order as many T-shirts as can fit...).
例:I want to order 1 container's amount of baseballs.
ご参考いただければ幸いです。