Hopefully someone can answer if you'll need it or not, but your cheapest, lightest options for a bowl and extra water containers involve a little dumpster-diving at the recycle center.
For a nice, big, very light bowl, cut the bottom 3 inches off of a 1-gallon plastic milk jug. It is MUCH safer to do that with scissors and not with a razor knife. If that is too big for you (if you can't nest it nicely with other gear), find a half-gallon milk or OJ container and use the bottom of that. If you only need it early in the trip, just throw it away when you're done with it. Whatever you source, run it through the dishwasher. HDPE plastic takes very high (>boiling) and very low (<-50F) temperatures and cleans up completely in the wash cycle.
And for water storage, 2-liter pop bottles are tough and also free in the recycling bins.