aspen doesn't generally-- even in july-- reach higher temps than 75. 80 on a very hot day. no humidity. pours down rain at about 3 or 4pm in summer. lasts a few min, then 20 min later you wouldn't know it rained had you not seen it with your own eyes. it's a very casual town. summer is shorts & flip flops & sundresses, for evening, dresses & heels, here's how to really stand out, and NOT in a good way: wear a business suit, wear real fur (that's how you spot someone from texas!), hair extensions & have your lips plumped out to THERE. aspenites are natural, light makeup, polar fleece for working out & don't have elaborate hair-do's.
Toiletries and Medical Supplies: SPF- i can not stress how !!important!! suncreen is- and i am not talking spf 15. i wear 75 and still get color if i get careless & forget to re-apply. bring something for your nose- i use vasaline to line my nose with since it's so dry, it cracks & bleeds. band-aids if you're doing alot of walking. NEVER be without water. water & sunscreen will be your survival kit. spf chapstick, too.
Camping/Beach/Outdoor Gear: depends on what you want to do while you're here, but they also do sell anything 'rugged outdoorsy' in most shops. in the winter i like the yakktraks to stretch over my shoes or boots to grip the ice (they're useless in snow). they sell them at the UTE MOUNTAINEER on mill st.
Miscellaneous: whatever you do, don't believe that being an obnoxious jerk makes you more important than everyone else, or will make you fit in. coloradans, aspenites in particular, are a very friendly, helpful bunch. and you generally won't find an american among them! don't complain loudly and/or yell at service people. it makes you look like a fool. most aspenites will make a point of stopping to help you if you are looking at a map or seem puzzled.