We’ve been trying to reduce plastic and trying to reduce the amount of weird things (BPA etc) that our kids are exposed to, but it’s really hard to give up the ‘sippy’ cup – that great object that allows kids to drink without spilling excessively all over themselves, their clothes and the couch. Sigg, found at reusablebags.com, makes a kid-size version of their aluminum water bottle, complete with a kid-friendly minimum spill cap and there are even handles you can buy to make it just like the regular sippy cups. They are cute too and there are a ton of different designs. They are not as cheap as the cups you can get at the grocery store, but we just wash the more often and try to pay attention to where they are. When we were using the cheap ones, it was easy to just buy more instead of searching out where our existing ones were.
As a side note, I use a bigger one of these for my water bottle and I love it too. Reusablebags.com is a great site for, you guessed it, resuable bags too!