Meaning of 的 in 我买了一些吃的。
You can think the "的" is implicitly to include the words - "Food" or something else for eat.

In Chinese, sometime we will skip the word in daily use.

For example:
我是买了一些吃的 =  我是买了一些吃的(東西)
It mean: I have buy something to eat, so that without (東西) also the same meaning as well, but actually it is not a formal grammar.

see one more example:
我做了一些好吃的 = 我做了一些好吃的(東西)
It mean: I have make something delicious, same as above, skipping the (東西) have the same meaning.

(東西) can be another words depend on what you refer to, it can be "飯/Rice", "蛋糕/Cake", "雪糕/ice-cream" etc.