I think everyone needs a bit of trial and error to figure out what they need. A lot of it is just personal preference. I know people that think tents are for suckers--they use ultralite hammocks. (not me) The same people don't filter water (you can generally get away with that here but again, not me). Ohers couldn't live without bringing everything but the kitchen sink.
If it's just you carrying everything, I'd get the lightest you can afford that still works for you whether that's one or two man. (Some of the 2 man tents are so small, I would really consider them appropriate only for one person+stuff). It really does take some research to figure out what the best combo of weight, functionality and price is. Ultralight is great but sometimes it means sacrificing nice features, and sometimes it costs a fortune. So there is always compromise. Set it up in the store to make sure it's not a pain in the ass. Assume you will be setting this up in the dark when you are cold and hungry at some point. Make sure there is room for your pack and boots either in the tent or under a vestibule, in case you need to protect them from rain overnight.
something to purify water?
For 20 years I've just used a PUR filter, the kind you pump into your water bottle. Super easy, not too heavy. There are plenty of brands out there. Some people bring a couple iodine tablets as an emergency backup. I'm interested in those pens but haven't used one yet.
Backpacker Magazine is a great resource. They do an annual gear guide, and have a lot of info on their site. Check out their Editor's Choice picks.
https://www.backpacker.com/gear-zone-editors-choice-2011/gear/15461
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Since Pequenita did the work of putting together a list, I'll just work from that and tell you what I bring. Like I said earlier, a lot is just personal preference.
GEAR
backpack
backpack rain cover and garbage bag/dry bags in bad weather
(I've never needed this, and I backpack in the PNW. My stuff has always stayed dry in my pack. But, I also check the forecast before setting out--I would not go if it was a weekend of rain ahead)
trekking poles
(optional--I'd bring these only if you have knee issues. They can be really helpful but on brushy or rocky trails, they can also be extremely annoying)
daytrip bag? (optional)(
get a backpack with a removable top)
tent (and fly)
Here in the NW I also use a groundcloth, which we actually use inside the tent, but many people will tell you this isn't necessary, that your tent bottom is waterproof and durable
sleeping bag (appropriate for weather forecast)
(plus liner if cold weather)
(I bring a 0 degree bag, no liner. If you're a woman that's always cold, like me, the ratings are a joke. They are definitely rated by big sweaty men
sleeping mat/air mattress & repair kit
I like the full length prolite Thermarests. 3/4 length are lighter, but don't keep you as warm
(bring extra pad/thick pad for snow camping)
water bottles
water filter (& scouring pad), sterilite pen, and/or iodine
(I bring a filter only)
headlamp/flashlight & extra batteries
(I bring a headlamp only. My headlamps die before the batteries do)
stove, fuel, and pot(s)/pan(s)
(I like the Primus or Snowpeak type system--cheap, easy, you can buy the fuel anywhere, lasts forever: https://www.rei.com/product/636832/primus-yellowstone-classic-trail-stove)
lighter or stormproof matches
bear canister (in bear country)
(I don't think in CO you will need more than a regular bear bag, or an Ursack if you want to get hardcore. Canisters are super heavy)
map in ziploc bag
compass
alarm for early AM summits
Bear bag--maybe you don't need an actual bear bag in CO, but you do need to at least protect your food from critters. We only use our sleeping bag stuff sack and some thin rope. You can google how to hang a bear bag. There are actually lots of things that are not great about this system--mice can still get to your bag, for instance--but I've used it for 20 years as do most people I know. I do mean to get an Ursack, though--that's way easier in subalpine or alpine areas where big trees are scarce
FOOD
While dehydrated food is nothing to write home about, I have zero interest in cooking in the backcountry. There are real issues around doing dishes in bear country; even if there aren't bears, food bits attract rodents and other creatures you don't want. Also I am generally tired and dirty. So, open pouch, dump in water, stir and eat. Zero cleanup. The empty pouch goes in the bear bag. There is lots of info online as to which brands are edible and which aren't.
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Isn't it funny how much gear we need to "rough it"? I always give my husband crap for all the gear he takes fishing--how much stuff does a person need to take to catch a little fish?--but really, this is no better. *sigh*