Plastic pill and medicine bottles are fantastic for reusing for walking. They're waterproof, and the perfect size for carrying small amounts of whatever.
I just wash mine thoroughly with detergent, and soak the labels off. I usually have to use a bit of eucalyptus oil to get the labels off properly.
Here's some of the small collection that I'm using:
An old-school trick used to be to re-use plastic film canisters for keeping matches dry, but the advent of digital cameras has put paid to that one. Luckily I've still got a few that I've kept for years - it came in handy just over Easter, actually, when the box of matches got wet.
**** EDIT ****
In response to some concerns properly raised about the safety of reusing materials as food containers, I have found some relevant information.
The plastics concerned are HDPE (high-density polyethylene), which is used for anything from medicines, to detergents and milk. Material I found on the web suggested that the primary danger with reusing these plastic bottles is from not washing them properly, leading to bacterial contamination.
Leaching of potentially toxic or carcinogenic chemicals didn't seem to be a problem.
According to one report:
Additives in LDPE (low-density polyethylene) & HDPE (high-density polyethylene) are primarily antioxidants, such as Irganox or BHT2. There is little information on the toxicity (inluding endocrine disruption) of these compounds, but we could find no evidence of toxicity. There is some evidence that they are not endocrine disruptors or estrogen mimics.
"polyalkylated, hindered phenols like BHT and Irganox 1640 (Ciba-Geigy, Basel, Switzerland) are not estrogenic, while being effective antioxidants..."
Interestingly, there is some recent work developing tocopherols (Vitamin E) as antioxidants for HDPE & LDPE.
Migration into water and food substances have been measured for these antioxidants, generally at higher temperatures than experienced in normal use. At high temperatures, and especially with fatty or oily foods, there is considerable loss of antioxidants. These plastics should thus be used primarily with cold water, to reduce migration to a minimum. Washing agents and other substances used in the manufacture of the polymer may be present, but can be removed with thorough washing of the new plastic product. HDPE generally exhibits the least migration of antioxidants.