1) Avoid large amounts of caffeine. Watch out for it hiding in unexpected places. Check labels to determine dosage. L-America is perfectly okay with selling caffeine in amounts that occasionally kill people and frequently make people sick.
2) Do not mix caffeine with large amounts of sugar, especially just one kind of sugar. Most energy drinks and coffeehouse menus could be summarized as "crash in a cup." O_O
3) Buffer caffeine and sugar with things that take a longer time to digest such as complex starches, healthy fats, and protein. At coffeehouses, look for a multigrain muffin, nut'n'seed bread, or whole-wheat bagel with cream cheese and/or lox.
4) Look for action snacks designed with a multipeak sugar profile. That is, they use different types of sugar that break down at different speeds, so there's a fast, middle, and slow peak creating an overall moderate curve instead of a narrow peak-and-drop.
5) Consider consuming healthy foods that boost energy and mood. Smoothies offer a way to add fruits and vegetables, along with any supplements you want. Many junk foods and beverages create the illusion of a boost but then drop you off a cliff. O_O There are other things that give your body a genuine boost with little or no crash. Remember that your lizard brain is stupid. It believes that sugar, fat, and salt are always good because they used to be hard to get and it can't adapt quickly. You know better, so you have to do the thinking for your lizard brain.
6) If you are consuming caffeine and sugar to cope with stressors, consider using adaptogens instead. These help your body cope with a wide range of challenges.
7) Pay attention to how you feel after you eat and drink. Note which things make you feel better or worse. Consume more of what makes you feel better and less of what makes you crash.
Here are some other ideas for avoiding a caffeine-sugar crash.
Once it happens, know how to treat a caffeine crash and a sugar crash. Remember that an ounce of prevention is worth a pound of cure.