Hamstring stretch
This one is old school, but it works. Sit down and spread your legs wide, reaching to each foot while holding a stretch. Then kick your feet in together and bend forward. This will also help you stretch out your lower back (important if you’re carrying the extra weight of a hydration pack!)
I do not stretch, ever (unless you count a quick bending at the waist and reaching to the sky, and bouncing on my tip-toes, which takes about 30 seconds). I once hurt myself stretching and couldn’t run for 2 weeks. I always do a warm up. I know there’s proper way to stretch and a wrong way, but I’d rather not risk it anymore.