Welcome Stacy!
You can get a bear canister at the Visitor Center in Lone Pine where you pick up the permit, or at the Portal Store. One should be fine for two people on an overnight trip. Share one, and split the weight. Maybe the other person carry a 2-person tent.
Down or synthetic? Down is lighter and more expensive, must be kept dry. Synthetic keeps more heat in than down if the bag gets damp.
Share the tent, share the weight.
Stoveless works. Some ideas for food: Granola bars, granola cereal, trail mix/nuts, etc. Tortillas and peanut butter (bread gets mashed down). Bagels.
Be sure to read through the Orientation Notes (link is above and left). Think about acclimating at least one night at altitude before you start your hike.
