Tanks
Sun's out, guns out. Everyone's heard of the saying, but a lot of guys do live by this motto. Any tank is great for warm weather to even out tan lines and show off those bis and tris. Stick to a nice tropical themed tank and you'll be dying for spring break to arrive. PacSun and other surf-themed retailers are always good places to shop at to pick some up.
Polos
Polos are classic pieces to any undergrad's wardrobe. Mostly, you'll see guys wearing ones from Vineyard Vines, Polo Ralph Lauren and Lacoste. But wear them accordingly, though. Understand the difference between slim fit and regular fit, and know which fit suits your body the best. Any color will do, but lighter tones are the way to go in spring. Pair it with a pair of khakis and you'll be good to go.
Shorts
Feel comfortable in the shorts you're in. Don't wear them too tight, but, please, don't wear them if they're too baggy. Something in between works perfectly. Cargos are a fraternity member's worst nightmare, but it's okay, they won't harm anybody. Shorts that end a few inches above the knee work the best. Pick a solid color like khaki or navy, but don't be afraid to wear a pair that sticks out and makes a statement. Bonobos and Chubbies are notorious for their extreme shorts, so wear them with pride.
Shoes
Low-top vans
Boat shoes
Loafers
Chacos
Rainbows
Sanuks
Nike Rose Runs
adidas Ultraboosts
Any low-top sneaker is perfect for warm weather. It weighs less than a boot, and can be taken off easily when it's time to take a dip in the pool.