What you are proposing is excellent - for some conditions, not so much for others. Preventing and treating hypothermia is all about skills and knowledge, and not so much about "gear."

The classic PSK and "ten essentials" equipment lists are basically all about hypothermia and its evil twin, hyperthermia. Interestingly enough, staying hydrated is critical to avoiding both states.

What you need can vary from something the size of a belt pouch to the entire contents of a 6,000 cu in pack. Basically you want clothing and shelter adequate for conditions, and then just a little bit more. My irreducible minimum extra clothing that I have always carried for years is a light coated synthetic hooded shell. The present version weighs all of 4 oz, but it will provide crucial wind proofing and allow rewarming. It doesn't get used very often, but when it is employed, the circumstances are memorable.

The ability to provide hot food and drink is important; again, my minimum kit can fit inside a sierra club cup, but when it gets cold I carry much more. Life as we know it is impossible without the proverbial nice cup of tea.

Remember -"There is no such thing as bad weather, only bad clothes." Another line I just ran across from my bible, "Medicine for Mountaineering" by Wilkerson - "A human's greatest protection against the cold is his intellect."

Read extensively in the literature on hypothermia and/or take a good first aid course.