I never carry more than one camera and one lens. My kit is so small that it's always ready to go: FM2 plus either 16mm, 20mm or 35mm lenses.

I often find that the SLR is too bulky and then I'll take a small Olympus: 35RC, XA or MJUII.

Normally I have two spare rolls of film with me: Neopan 400/1600 or Superia 800.