Ingard here, the school I send my youngest daughter to encourages resealable, reusable water bottles for the kids at their desks.
This would be personalized, recognizable, convenient and less likely to be lost. 
Get the stainless steel customized water bottle from Ink Garden for $3 plus
Shipping (Shipping is $5.99) for a total of $8.99 SHIPPED
USE Code:BOTTLESALE
I had a little fun loading pictures I had on my computer already and adding words.
Here is the subtotal before shipping and after the code: BOTTLESALE