The appropriatness of cotton depends on where you hike. In the PNW or on the California coast, planning on not getting wet is a pipe dream! If you do off trail travel bushwhacking early in the AM or after rainstorms you WILL get wet. I have nothing against someone hiking in cotton, AS LONG AS they have sufficient non-cotton insulating layers to change into. Personally, I do not want to carry the extra weight of cotton plus insulating layers. If you get 2-3 days of rain in a row and cotton gets wet, you will end up carrying around dead weight. Jeans are not appropriate for hiking for other reasons- they are very heavy and they tend to be tight in the knee area which makes you work harder for each step you take. If you want to hike in cotton pants they should be loose enough that they do not bind when lifting your leg up over a rock.
I use an Arcterex 24L pack for day hikes. But I do not have a large amount of camera gear. The 24L pack was my go-to pack for long day technical rock climbs. Black Diamond targets climbers so their packs have extra loops for carrying climbing gear or crampons, ice axe, etc. If you do not need these features they just add weight. I like Arcterex because you can order their packs in different waist sizes vs pack size. The packs are also bomb proof. Arcterex packs are also specific to climbing. IF you are not going to do climbing or scrambling where your pack gets beat up by rock, the climbing-specific packs are overkill and too heavy.