Coilless safety pins (pictured below) and split ring stitch markers both work.
You can even snip a short length of yarn and fish that through to mark something. Since you likely know where to find yarn, it can be an easy way to mark something in a pinch. And, it’s super-cheap too!
Be sure to have a sharp pair of scissors and make sure that you save them just for your crafting.
While growing up, my mom had regular scissors and then craft scissors. We knew better than to use the craft scissors for anything like paper.
The scissors don’t need to be big either. Most of mine are maybe 3 inches in total. Nice and compact so they easily fit into my bag.
A way to measure
The easiest thing is to keep a retractable tape measure. But, if you’re anything like me, you’ll be sure to lose track of it.
In a pinch, lots of things work. I suggest you learn the measurements of your phone since you likely have that with you all the time.
This is just a sampling of what’s in our Crochet 101 PDF!