San Diego in February

Merino or synthetic, since this is the layer that sits under everything else and cotton stays wet.

PatagoniaPatagonia Capilene Cool Merino Blend Long-Sleeve - Women's$62.30Shop at Backcountry →SmartwoolSmartwool Merino Sport 120 Long-Sleeve Shirt - Men's$85Shop at REI →IcebreakerIcebreaker Merino 125 Cool-Lite Sphere III Long-Sleeve - Women's$100Shop at Icebreaker →ColumbiaColumbia Tech Knit Long-Sleeve Crew - Men's$27.49Shop at Columbia →

Merino, not cotton. It stays warm when it's damp and still doesn't smell on day three.

Arc'teryxArc'teryx Women's Satoro Merino Wool Crew Neck Long-Sleeve Base Layer Top$95.73 was $120Shop at REI →REI Co-opREI Co-op Women's Merino 185 Long-Sleeve Crew Base Layer Top$84.95Shop at REI →TerramarTerramar Men's 3.0 Merino Bi-Layer Long-Sleeve Crew Base Layer Top$29.73 was $45Shop at REI →Arc'teryxArc'teryx Women's Lana Merino Wool Crew Base Layer Top$63.93 was $90Shop at REI →

One pair for every two days, plus two.

SmartwoolEveryday Merino Bikini Underwear - Women's$34Shop at Backcountry →SmartwoolEveryday Merino Thong Underwear - Women's$34Shop at Backcountry →REI Co-opREI Co-op Women's Merino Hipster Underwear$29.95Shop at REI →SimondSimond Trek 500 Merino Wool Backpacking Underwear Women's$29.99Shop at Decathlon →

Trail runners dry overnight where boots take days, which is why most people prefer them on warm trails.

CraftCraft Women's Endurance Trail-Running Shoes$130 was $175Shop at REI →KiprunKiprun Kipsummit Max Women's Trail Running Shoes$150Shop at Decathlon →KiprunKiprun Kipsummit Men's Trail Running Shoes$130Shop at Decathlon →QuechuaQuechua Men's MH100 Hiking Shoes$45 was $64.99Shop at Decathlon →

Buy it used: REI Re/Supply sells gear like this for less. See used gear

Bring the pair you already walk ten miles in. Brand new shoes on day one is how the blisters start.

NnormalKjerag Shoe$109 was $140Shop at Backcountry →SaolaQuito Shoe - Men's$130Shop at Backcountry →New Balance530 Shoe$60.47 was $110Shop at Backcountry →SaolaEzo Shoe - Men's$83.96 was $120Shop at Backcountry →

Polarized kills glare, but the tag has to say 100% UV separately, and that's the part your eyes need.

SmithSmith Era ChromaPop Polarized Sunglasses - Women's$113 was $189Shop at Backcountry →ZealZeal Isabelle Polarized Sunglasses - Women's$67.03 was $149Shop at Backcountry →CostaCosta Caleta Net 580G Polarized Sunglasses - Women's$174 was $248Shop at Backcountry →ZealZeal Bennet Polarized Sunglasses - Women's$59.60 was $149Shop at Backcountry →

10,000mAh is about two phone charges, 5,000 barely gets you through one long day.

Top pickGoal ZeroGoal Zero Venture 75 Power Bank$120Shop at REI →BioLiteBioLite Charge 80 PD Power Bank$99.95Shop at REI →AnkerAnker MagGo Power Bank (10,000 mAh, Slim)$80Shop at REI →AnkerAnker Zolo Power Bank (20,000 mAh, 22.5W, Built-In USB-C Cable)$40Shop at REI →

REI members usually get 10% back on full-price gear. Membership is $30, once. How it works

65W or more charges a laptop. Anything smaller only keeps up with phones.

Peak DesignPeak Design 65W Dual Slim Charger$64.95Shop at REI →Peak DesignDual Slim Charger$64.95Shop at Peak Design →AnkerAnker Wall Charger (33W, 2-Port) with USB-C to USB-C Cable$25Shop at REI →AnkerAnker MagGo Wireless Charging Station (3-in-1, Foldable Pad) with Charger and USB-C Cable$100Shop at REI →

35 to 45 liters fits most cabins. Check your airline's size limit first. Most won't take much over 40L in the cabin.

Top pickMatadorMatador 45L Global Travel PackSee price15% off with CHRISANDSARAShop at Matador →PacsafeGo Carry-On 44L Backpack$180Shop at Backcountry →Osprey PacksOsprey Packs Archeon 30L Backpack$132 was $265Shop at Backcountry →MatadorMatador GloberiderSee price15% off with CHRISANDSARAShop at Matador →

Hard shell protects what's inside, soft shell squeezes into a tight bin, and either way check the size with wheels included.

CotopaxiCoraza Suitcase - Carry On$295Shop at Cotopaxi →SamsoniteHyperflex ∞ Carry-On Spinner$126 was $180Shop at Samsonite →SamsoniteFreeform Spinner$154 was $220Shop at Samsonite →Peak DesignRoller Pro Carry-On$600Shop at Peak Design →

15 to 25 liters.

MammutLithium 20L Daypack$135Shop at Backcountry →CotopaxiConsuelo 22L Daypack$120Shop at Cotopaxi →CotopaxiElqui 24L Daypack$100Shop at Cotopaxi →Osprey PacksOsprey Packs Arcane Large 20L Daypack Botanica$65.97 was $110Shop at Backcountry →

Get locks marked TSA approved. Security can cut anything else off to search your bag.

MatadorMatador BetaLockSee price15% off with CHRISANDSARAShop at Matador →PacsafePacsafe ProSafe 620 TSA Accepted Luggage Locks$17.95Shop at REI →KnackKnack TSA-Approved Lock$16Shop at Knack Bags →Osprey PacksTSA Cable Lock$15.95Shop at Backcountry →

It runs on Find My, so this one's for iPhones.

AppleApple AirTag (2nd Gen, 4-Pack)$95.99Shop at B&H Photo →eufyeufy SmartTrack Link (2-Pack)$19.99Shop at B&H Photo →AppleApple AirTag (2nd Gen)$29Shop at B&H Photo →

Going in the water, buy the 80-minute one, since 40 minutes is barely one swim.

BadgerBadger SPF 50 Adventure Sport Mineral Sunscreen - 2.4 oz. Tin$18.95Shop at REI →Blue LizardBlue Lizard Sport Mineral SPF 50 Sunscreen Lotion$14Shop at REI →Sun BumSun Bum Mineral SPF 50 Sunscreen Face Stick$14.50Shop at REI →ThinksportThinksport Clear Zinc Active Face SPF 50 Sunscreen$15.95Shop at REI →

Rechargeable over USB-C, so it shares a cable with everything else you carry.

FenixFenix HM50R V2.0 Rechargeable Headlamp$59.95Shop at REI →BioLiteBioLite Dash 450 USB-C Rechargeable Running Headlamp$69.95Shop at REI →BioLiteDash 450 Rechargeable HeadLamp$69.95Shop at Backcountry →Black DiamondStorm 450 Headlamp$38.47 was $69.95Shop at Backcountry →