1. If you do not have a cocktail shaker, you can use two glasses, one slightly smaller than the other. Pour the ingredients into the larger glass and place the open end of the smaller glass into the second. (I would recommend a plastic cup for the smaller cup.) Make sure to tap the top to ensure there is a seal. Shake lightly and remove the top cup. If the seal seems hard to break, tap the side of the glasses where the seal is formed.
2. A third alternative for the shaker is to use a cup or jar that has a lid (such as a mason jar).