They should make it so that you can pay for both in one area.
It would be nice if you could pay for both groceries and thing from the pharmacy at the same cashier/check out.
この場合、次のように言うと良いと思います。
ーThey should make it so that you can pay for both in one area.
「両方を一箇所で払えるようにするべきだ」
ーIt would be nice if you could pay for both groceries and things from the pharmacy at the same cashier/check out.
「食料品と薬局の物を同じレジで払えたらいいのに」
ご参考まで！
At the supermarket, they should have put the pharmacy and grocery section within the same area, that way you could pay together in the same register.
ご質問ありがとうございます。
「一緒にすればいいのに」はそのまま英語で「They should have done it so it could be together」と言います。
また、「スーパーで同じエリアに薬局と食材エリアが分かれてて、会計場所を一緒にすればいいのに」と説明したいなら、そうすると、「At the supermarket, they should have put the pharmacy and grocery section within the same area, that way you could pay together in the same register.」になります。
ご参考になれば幸いです。
カナダ 
アメリカ合衆国 
