S.H.
Just use a Sharpie pen. Get different colors.
And also get the "Sharpie Rub A Dub" laundry marker for clothing.
Get the fine point and regular point, Sharpies.
This is the easiest way, the least expensive way to label and it lasts.
If on water bottles, and it wears of due to washing, I just re-write my kids' name on it, or their initial. And that's it. Easy.
I label ALL my kids' things, with Sharpie pens.
It works.
Super easy.