や
and (among other things)
Noun + や + Noun (+ など)
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や joins nouns like と, but hints that the list isn't complete: パンや卵を買いました, "I bought bread, eggs and so on". と says "these and nothing else"; や says "things like these".
It often ends with など, "etc.": 犬や猫など, "dogs, cats and the like". Even without など, the "and others" is understood.
Use it when the items are examples. If someone asks exactly what's in your bag and you answer with や, it sounds like you're leaving something out on purpose.
Examples
冷蔵庫に肉や野菜があります。
There's meat, vegetables and so on in the fridge.
休みの日は本や漫画を読みます。
On my days off I read books, manga and things.
京都や奈良などに行きました。
I went to places like Kyoto and Nara.
机の上にペンやノートなどがあります。
There are pens, notebooks and so on on the desk.
朝はパンや果物を食べます。
In the mornings I have things like bread and fruit.