Get some panniers like Jandd Saddlebags and eliminate everything that wont fit. They're not waterproof, but can be coated w/Thompson's Watersealer inside and out to great effect. 3 coats minimum. But, still double wrap the contents if knowingly riding in rain. And I'm a +1 about keeping shoes at work. Along w/some foot spray. Depending on one's job situation one can keep several shirts, pants or shorts, socks, briefs, jackets, etc. Personal items like deo, toothpaste and brush, cologne, soap, towel(s), etc as well. This greatly reduces what one has to carry on a daily basis.