You may struggle to find a sleeping bag in Kigali. Nakumatt in the UTC has a small selection of camping equipment.
Not a huge amount to do in Kigali if you are already seeing the Genocide Memorial. You could do a day trip to Nyamata and Ntarama churches (also genocide memorials), or just have a wonder round the city, craft markets, lunch, drink in the garden at Milles Colines etc, it's quite a pleasant city for strolling.
If your Saturday is the last Saturday of the month not much will be open before noon and there will not be much public transport as it is Umuganda (sp?) when everyone has to do community service.