Best non-leaking drink container for lunch boxes?

Yeah, so I am already on the back-to-school hunt for supplies, b/c the sales started today. Do any of you with kids who pack their lunch, have a drink container you'd recommend fulfilling the following list of requirements:

a) Easy to open and close (rules our our KK, the tops are a PITA)

b) Doesn't leak (rules our our thermos funtainers, which leak when they are not standing up)

c) BPA free

d) Not excessively big (needs to fit into a LL Bean Critter lunchbox along with his food containers)

Thanks!

Oh and have any of you tried the, "Fuel" brand containers at Meijer? I know they are BPA free and are reasonably priced, but wondering how leak proof they are. They seem easy to open and close nicely and come in a nice selection of colors.

The Rubbermaid litterless lunchbox small size are OK. I use them for milk in DD#1's lunchbox. I pack it in her backpack so that the milk container stays upright.