Though sleek, store-bought shakers work well, you can use items already in your kitchen to shake beverages. A shaker helps you blend and chill a drink, so any vessel and with a way to secure its top will work. As long as your drink is shaken and your clothes remains dry, your DIY shaker qualifies as a success.
Use two cups, one with a slightly smaller mouth than the other. Add your drink ingredients to the bigger cup, firmly fit the smaller cup upside down into the larger cup's mouth, hold each end tight and shake. Simply create a small opening between the two cups to strain the drink out. This design actually reflects the origin of the modern cocktail shaker.
Flip the two-cup DIY drink shaker when making drinks with lots of ice. Put your ice and drink ingredients in the larger cup and place a smaller cup, right side up this time, into the mouth of the big cup. Keep the cups upright, shake in a circular motion and strain into a glass. This method gives you a little more leeway with cup sizes. Use glasses rather than plastic cups for better cooling capabilities.
Use a travel coffee mug in a pinch. Add your cubes and drink ingredients, put the lid on securely, place your thumb over the lid's opening, shake and pour. Use a metal mug if possible, as metal cools iced cocktails better than plastic. You can also use a thermos, as long as it has an opening big enough to fit ice cubes for chilled drinks.