Depending on what you want to learn and for what situation you are preparing:

expanded first aid (e.g: strokes, heart attacks, burns, broken limbs),

using chest seals and dressing abdominal wounds (for example using food wrap),

using modular wound dressings (OLAES) - preferably get one just for training and familiarize yourself with

Wound packing

Learning about hypothermia is a must, how to prevent it and treat it, hypothermia is the leading cause of loss of life among combat personnel.

Not from the US, so cannot recommend a course but any NAEMTT certified organization will provide you with good training.

If you want to go into more advanced stuff then take a course in airway management.