Welcome. What you carry really depends on the weather. There are a few gear lists here that may be helpful. Look for links to them on the main page of the site (not the forums, the actual home page.
I've carried a small multi-tool in winter, but just a SAK (Swiss Army Knife) otherwise. Mine has a few tools on it, but is one of the smaller ones.
Pants-very much a weather dependent item. I have a light pair of rain pants I wear in winter, otherwise, shorts. I've hiked in long johns and a pair of surf shorts in rainy weather.
Stove-for beginners, I always recommend a canister stove. Alcohol stoves are fine and you can make one of a hundred different designs relatively easily and cheaply, but a canister stove is a no muss, no fuss kind of stove. I have one, along with some others.
Wicking base layer or long johns-to me, two different items, one for warmth, one for hot weather (like a Coolmax). For cold weather, I wear Capilene from Patagonia. Expensive, but my first set has been in my closet for close to 25 years. I just bought a new top-expedition weight. Got it on sale, half price.
Water filter-one of the most hotly debated subjects around. For now, tablets will work for you until you decide if you want a filter and then, which one. There are hundreds of posts on the subject on this site alone. You can use the search function to find them. Read my post on using search in the General Discussion forum.
Don't get me started, you know how I get.