There's are only two things that I always have on me when I'm shooting film. The first is a camera loaded and the second The Sekonic L-308S is one of them. I actually started out with the more complicated and feature rich Sekonic L-358 but sold it because I never really used the flash sync and studio features. The basic Sekonic L-308S is a perfect shape, able to slip into my pocket pretty easily and barely larger than a deck of cards.
In use it's extremely simple, I usually keep it in ambient mode and take a reading of shadows and direct light. If the emulsion is versatile I'll just set my settings for shadows and overexpose the film a few stops. In cloudy weather where exposure is constantly changing, I'll remeasure my exposure whenever I think there's a large shift in light.
The device is pretty durable being able to take drops and get bounced around without affecting use. It also doesn't break the bank and can be had for around $50-$100. I got mine through a Craiglist purchase and wouldn't be surprised if there aren't a few available in your town as well.
It's rare in photography when a great tool doesn't come with a high price tag. When shooting film being able to know your exposure is correct and you are not underexposing frames is great insurance. The simple and affordable Sekonic L-308S delivers on that promise every time.