Lets face it if you are hiding from Zombies as a group in a confined area, eventually you will have to take a Bio-Break.
One solution we talk about at the camp is a Wag-Bag (a bathroom in a bag)

Each Wag Bag kit contains

• WAG BAG waste bag, zip-close storage bag, toilet paper and hand sanitizer
• Disposal bags contain environmentally friendly Poo Powder™ that quickly turns human waste into a solid for easy transport and safe disposal
• Poo Powder treats up to 32 oz. of liquid and solid waste, allowing for multiple uses per bag – do you share well with others?
• Odor neutralizer eliminates unpleasant odors; decay catalyst initiates decomposition

Landfill-approved WAG BAG waste bags are biodegradable and can be disposed of in trash with regular garbage
I think Poo Pourri may be a good addition to your Wag Bags in your kit.