We searched high and low for cheap water bottles, since we know we won't have them for long; found these metal ones for $4. We bought two even though we know they will likely leak. Frankly, in my experience, so do the $20 ones once they've been dropped and bounced, as what tends to happen.
Next, I bought an oil paint Sharpie marker to doodle on them with, so they would stand out among the plethora of water bottles at school. One has my crazy doodles of a submarine and the other a trailer in the field. The latter has a sunrise coming up from behind, which I had to explain to Spud when he asked what the big spiky thing on the trailer was. I definitely didn't get too precious with my doodles ... because I'll never know when I may never see them again.