Carrying plastic bags is a no-no when entering Rwanda. The border police, when on road travel, will ask you to discard any plastic bags you have and transfer all your stuff in a paper bag or be prepared to throw them in the trash lest you carry them bare. Not to worry though, there are enterprising people selling paper bags at the border, just be ready with your Rwandan Francs, though some are willing to accept Kenyan Shillings.
Kigali is the capital of Rwanda and throughout the city and its immediate suburbs, you will notice that the locals are making a serious effort in keeping their place neat and tidy..no litters! I think it is the cleanest place in East Africa.