Hi there,
Thank you for reaching out to us! It's great to hear you are interested in the Reaction Tackle 2-in-1 Sling Bag/Backpack.
To answer your questions regarding the Small size:
Capacity: The main compartment is designed to hold up to two (2) tackle boxes.
Box Size: It is perfectly sized for 3600-size tackle trays (also commonly referred to as "Medium" utility boxes).
This compact size is a fan favorite for "pond hopping" or light travel when you want to stay mobile without carrying a bulky bag. If you find you need a bit more room, our Medium version holds two 3600 boxes with extra room for gear, and the Large version can accommodate up to four 3600-size boxes.
You can find all the options and additional photos here: Reaction Tackle Sling Bag/Backpack
Please let us know if there is anything else we can help you with!
Best regards,
The Reaction Tackle Team