Getting a fire going in cold and wet conditions can be a real struggle, and one that can put your life in danger due to hypothermia if you're not adequately prepared. Obviously, the ideal solution is to bring energetic, water-resistant fire-starting supplies (such as waxed tinder wick, fatwood, or Vaseline-coated cotton balls) with you at all times. But preparing only for the ideal scenario is foolish — you should always have backup plans in mind.
Dig through your survival pack, and you'll find a variety of petroleum-based plastic and rubber products. While burning these materials in large quantities creates black smoke and may not be friendly to Mother Nature, doing so in small amounts can help you get a fire going. Potential combustible materials include disposable plastic bottles, food wrappers, rubber gloves, shreds of tape, or ranger bands. Some will ignite easily, while others will be more resistant, but when they burn they'll usually do so with a strong flame.
In the following video, Dan from Coalcracker Bushcraft demonstrates one source for synthetic tinder that you may not have considered: a knife sheath. Specifically, he's using the 90-degree spine on a Mora Basic 511 to scrape small curls of plastic off its hard sheath. Although this damages the sheath, you could easily use this method multiple times without completely ruining it — and as Dan mentions, this is an emergency measure, not one you'll be using constantly. Plus, the Basic 511 is only $8, so buying another one won't exactly break the bank.
If you're interested in learning more winter fire-starting methods, check out our previous article on Advanced Fire-Starting Techniques in Cold Weather.