Most behavior charts are intended to improve your child's performance over time, or provide weekly motivators for staying in line. Sometimes, though, you need to reward behavior in the short-term -- making it through a church service, maybe, or surviving a mall trip. Using a chart to break down the activity into small rewardable units of time can make it easier for your child to get it done.
Start by figuring out a reasonable time period for your child to go without a reward. For a very young child or a child with severe behavior issues, it may be as little as five minutes. Let your child know that for every five minutes of appropriate behavior, he will get a reward. It might be a sticker on a piece of paper, or a small edible item, or a coin, or a few moments with an obsessed-about item. If the behavior during any specific increment doesn't cut it, the reward is missed, but the time resets and the next increment of time is open for change.
This may be a chart in spirit only, if you're implementing it on the run and don't have time to write something out. But if you use this method often, or your child particularly responds to the idea of checking things off a chart, try drawing up a simple grid with the time limits you've determined, and make some copies to carry around with you. (Download this grid, if you like. It has fifteen boxes that are big enough for filling with stickers or notes.) You can do this on the fly, too, if you keep a small notebook with graph paper handy in your bag of tricks. It may seem like a bother, but if it buys you good behavior, it's worth it. And you'll get a star on your parenting chart.