A common alternative to PVC is low density polyethylene (LDPE), it's not as clingy as PVC plastic wrap, but it does not contain toxic additives that PVC contains. Brands like Glad Cling Wrap or Handi-Wrap are LDPE-based. Saran Premium Wrap, a newer version of Saran Wrap, is based on LDPE as well. I would still be very careful about what you do with plastic wrap over an enclosure housing your herp. What I use instead of plastic wrap for holding heat and humidity is a damp face cloth sprayed with de-chlorinated tap water.