comfy shoes
jacket
money
bus schedule
tiny radio
lots of friends

Gatorade drink mix packets are actually rather bulky. I know, I packed a 3-week supply for a volunteer trip to Ecuador, and they took up a lot of space. Recently I discovered Propel drink mix packets in the grocery store and Walmart, stocked near the Iced Tea and Crystal Light mix. Because they are non-sugar, they are much smaller and lighter, but still provide some vitamins and electrolytes. They also don't gunk-up the plumbing on sip-style bottles.

I tried some of those propel and others and while they are non sugar they all had nutrasweet or some other artificial sugar, they all gave me a bad headache like when a restaurant brings out diet soda by mistake.
I found packets of country time lemonaid and the single bottle packets of gatoraid are the same size.