If you work or work out in the early evening save your caffeine boost for the late afternoon. Coffee and a high carbohydrate snack then will power you through the evening. Experiment around to find the amount of caffeine and timing that work best for you. This is important since everyone is different in their response. Coffee has the most caffeine.
Tea has less and cola beverages the least.
The amount in coffee and tea varies greatly depending on the specific brand and brewing method. This makes it hard to get the same amount each time. Cola beverages always contain the same amount and you can buy caffeine tablets at any pharmacy. Some people maximize the drug effects by only consuming caffeine once a week. This is useful for one day or night of very high energy levels.