This is a really good question, and I'm sure the answer is different for everyone. Personally, I almost always carry a pair of period panties in whatever bag I take when I leave my house -- gym bag, hiking backpack, going to the grocery store bag. There's usually a tampon in there, too. If I'm actually ON my period, then there will be 1-2 extra of pairs of period panties in there, along with a tampon in case changing my underwear is inconvenient (like when I go on a hike).
I can wear the Thinx super heavy panties for several hours without bleeding through them, so I feel pretty safe when I have two pairs of those with me. But I'll wear a tampon AND the period panties if I can't change my underwear for 8+ hours.
I also always have ibuprofen, my prescription Cox-2 inhibitor (another anti-inflammatory med), and rizatriptan (my migraine meds).
For fatigue, I've found that going gluten-free and avoiding ultra processed foods really helps my overall energy levels. My diet is plant-based with lots of whole grains, vegetables, tempeh/tofu, and long-fermented sourdough bread (when I do eat bread). I also make sure to exercise (like walking 3 miles on the treadmill) almost every day. In fact, when I get smacked with a wall of fatigue before my period, going out for a walk actually boosts my energy levels.
Last but not least, I prioritize sleep. I need 8 to 10 hours every night. I've had insomnia in the past, which I've talked to my doctor about. And we've figured out things that interfere with my ability to sleep, including menstrual changes and caffeine after 11 a.m.
Here are some other tips in case they're helpful: https://endometriosis.net/living/symptoms-experiences - Keri (patient leader)