I keep a Lara bar in my shoulder bag pretty much all the time. On trips, I pack a bit of emergency chocolate as well. A timely snack can make a big difference for me.

Emergency food supplies are VERY important. Hunger leads quickly to emotional crash. Fuzzy blankets to curl up and hot tea in can also be calming and useful.

Cheese and crackers or jerky are better than sweets for some. No crashy after.

Do bagels count as tricks?

I like to keep some emergency nuts around. In general, I will agree with everyone here that keeping a snack that works for you so that when you're hungry and low blood sugar you can eat something healthy that will make you feel better rather than junk that will make you crash can help immensely.

Nuts are a great emergency snack because they keep for a long time, they're not carbohydrate-based (no sugar crash, longer-lasting effects, though a delay to kick in), and they're better for you than most other snack foods. Plus, they usually have a decent dose of salt to make up for what you're sweating out playing drums.

Agreed with everyone on keeping an emergency snack on hand. I have found that when I do so, I don't even use it very often; just knowing that it's there helps a lot.

The other thing is realizing that I'm low on resources and feeling fragile. I can get to a point where I'm OK as long as I'm doing routine stuff, but I know that I will break down if I am confronted with anything stressful. Then I try to stay doing stuff I'm OK with (occasionally this means "just sit there") until I can get some food and/or downtime. If I can, I also let someone trusted know what state I'm in at that point, so they can buffer for me where possible.

I am also really, really in favor of emergency snacks -- my favorite is a dark chocolate bar with lots of nuts in it, but it can be nice to have something salty around as well. If this is not an option, orange juice or some other kind of really satisfying, healthy-feeling juice tends to help me a lot, and actually just plain water can be really good. Reminding myself to breathe and taking a few seconds or a minute to pause and just concentrate on using my diaphragm to keep the air moving slowly and deeply in and out of my lungs often helps, too. Sometimes instead of just breathing, I'll sing something softly to myself instead, but really concentrating on all aspects -- this can also be achieved by putting on the right music and really letting it affect you.