The box is smaller this time, so there aren't as many snacks compared to last time. Sorry about that.
この場合、次のような言い方ができますよ。
ーThe box is smaller this time, so there aren't as many snacks compared to last time. Sorry about that.
「今回箱が小さかったから前回と比べてお菓子があまり入ってないんだ。ごめんね」
「前回ほどお菓子が入っていない」ことは、次のように言うと良いですよ。there aren't as many snacks compared to last time
ご参考まで!