Building your own kit?
These are nice because they stay clean and dry, they are conveniently packaged for sharing. If you choose not to include these, substitute a roll of toilet paper in a ziplock baggie.
Single travel packs of tissues, standard size for for personal hygiene. Let’s be honest: you are not going to be worried about blowing your nose. The main need for these will be to wipe yourself if you have to poop. Bathrooms will not be usable and you should expect toilet paper to be in short supply.