As a product designer who loves outdoor activities, I'm more critical when it comes to select products. I usually buy a cheap used product when I just got into a new outdoor activity. (I'm always very broke and can't really afford outdoor products.) Then realized I got a really shitty one. After I got addicted to that activity, I usually dumped money to the second purchase. Luckily I got pro deal which has saved me tons of money. I'm definitely not the pro-level in any outdoor activity yet; can only say pro-consumer at best. This guide is for very beginner - who has no idea how to start.
It really depends on how fast you hike and how much stuff you're gonna bring. In summer, I would only bring a hydration pack with 2L water bladder and some energy bars for any hike under 8 miles. In winter, I would usually bring 25L so I can put my layers, gloves, or bennies. Regardless the activity, the first thing I care about backpack design is water bladder compatible. I've hiked with some friends still bring water bottle in their backpacks and have to take it out every time... Or some girls bring very cute backpack that has little ergonomic design.
Here are some brands I suggest:
Hydration packs: camelbak, Salomon
Day packs: REI (The range is too huge. Go to the store and try it out!)
Backpacking packs: Thule (NASA level engineered. Pretty expensive but worth it.)
Here's an article explaining how you choose a pack you need in details. I think it's for people have hiked quite a bit and become nitpicking about functionality and usability. Like I personally prefer hydration pocket separate from main compartment because it can leak and make everything wet. (It has leaked to my NIKON camera.....)
I didn't really have hiking boots when I was living around LA - the trails there were mostly pretty mild or well-paved. I felt the importance of hiking boots when it comes to rocky terrain. They protect my toes from rocks and higher-top supports my ankles (but not prevent you from spraining your ankles!) The reason why I suggest wear more rigid, higher-top boots for backpacking because the weight of the pack will make you unstable. I would bring two hiking poles with me to make my life easier. (I usually don't use poles for day hike since I like to go faster.) However, rigid high-top boots will restrict your movement. It will slow you down. So a low-cut trail running shoes or hiking boots are better choices when it comes to short and easy hike.
If you want to know more how to pack for a backpacking trip, check this article here. It describes what you should prepare in details and have some good suggestions.
I'm big fan of La Sportiva. My current shoes are Miura and I've tried Genius (pretty aggressive downturn, the rubber sole is slightly thinner and softer so you get better feel) and Katana (most of my friends wear Katana. It's great for bouldering and climbing.) When you try out climbing shoes, they should be tighter than your street shoes, like your second skin, but not too tight to make you painful. (Well I still need to take off my shoes after every climb. They are never comfortable enough for me to walk.) Try to do a heel hook and see if your shoes come off.
Sports climbing - the bolts are located on the rock and all you need to do is placing quickdraws on the bolts and loop the rope at the other side of quickdraws, you need a harness, belay device (ATC / grigri ), helmet (protect you from falling rock), rope (length depends on how long the pitch is. I got 70m 9.6 rope), personal anchor system / sling (hold you at the anchors) , quickdraws and carabiners.
Here are some brands I suggest:
Black Diamond : I have their rope and quickdraws
Petzl : I have ELIA helmet (the line is softer the shape is more feminine) and LUNA harness.
Mammut : My friend has 9.5 Infinity Classic - their rope has different weaving technology than BD. It feels smoother.
I had a BD Drop Zone crash pad. Tbh the reason I bought BD because I can get discount there and pick it up on the way to climbing gym. I chose this taco style crash pad because I don't like the gap between, but it's harder to fold. Crash pad is also a perfect mattress for camping - it makes me like outdoor boulder a lil bit more.