I think some of the things you might want would need to be created through the use of some substitute.

Soap is one of the simpler things to make, but there are also natural substitutes, some plants, that can be sued for cleansing.

As far as creating a leavening agent, you would be remiss to not have a yeast starter. It not only is a leavening agent, but it also create alcohol, which if you could distill would give you a good santizer and possibly some fuel. In both cases, it would be expensive, unless you could get some modern commercial equipment, but without the yeast, it's never going to happen.

Fertilizers are also easy, compost. Plants can require generally three types of fertilizers, nitrogen, phosphates and potash. In order, composted green matter, composted bone meal, and ash. Composting green matter is easy, and making a pile of the weeds you pull, lawn clippings, raked leaves, etc, and jsut letting it rot will do. Bone meal, I've not tried, but I believe it can be done by making sure the bones are dried, nothing but bone, grinding them into as small parts as possible, then letting nature digest the rest. Potash, burn some hardwood, use the ashes. Some reading on organic gardening might offer a lot of information this stuff.