The best "kit" would be a Wilderness First Aid course.
Then, skip the prepackaged stuff, and remember the basics (I love the "Start the breathing, stop the bleeding, treat for shock").
My daypack kit is focused on wound care and enough ortho to make it back to the car. Antiseptic to clean wounds (including cactus), bandaids, a couple of 4x4s, and a "Bloodstopper", and a roller gauze. A couple of strips of moleskin. A couple of Sting-eze pads. SAM splint. Tape. Motrin, Aleve and aspirin. Gloves and a breathing mask. It all fits in a little black ditty bag.
My call-out kit (I do wilderness S&R as a volunteer, and have been doing and teaching this stuff for over 20 years) has a LOT more stuff in it, but that's because I'm supposed to be a mobile emergency room. When it's just me -- I stick with simple and leave the call-out kit in the truck.
Snakebite kits are a painful and dangerous joke. Treat the affected limb like a broken bone, and get to antivenom (which you can not carry in a kit). While we still teach the constriction treatment, I've yet to see it done right in the field... and I think I'm up to 25 or 30 snakebite presentations.
I like the new waterfilters. They're reliable and effective. The straw thingies aren't overly effective, at least the ones I tested in the lab. The tablets take too long for me -- at least for day hikes. But, if you're carrying a bladder, you only need to worry about unplanned bivouacs, so throw in the tablets just in case and skip the weight of the filter.