With "casual dress", anything goes. Let your comfort and the weather be your guide. Still, it's important to use your best judgment. No matter how casual the dress, everything you wear should fit you well at your current weight, and be in good clean condition.
For the ladies
'Casual dress' for women can include fashion t-shirts, peasant and cotton jersey blouses, fitted sweaters, and other tops including sleeveless, tank, and halter styles. These can be paired with denim jeans, Capri pants, shorts, or skirts. Shorts and skirts should be mid-thigh length or longer. If in doubt, match these with complementary leggings. Knee-length and maxi dresses are both great if you aren't sure exactly how casual the venue is. Choose heels, flats, sandals or sneakers as appropriate.
For the guys
A casual dress code is a great occasion for designer tees and jerseys. Short or long sleeved button-up shirts are also a good choice, but even for casual dress an undershirt is a must. Denim is acceptable, as are shorts. For footwear, opt for sneakers, boots, sandals, deck shoes or canvas slip-ons. If dressing for an evening event, banish white athletic socks to the back of the drawer and go for black socks only -- ankle-length with shorts and sneakers, dress-length with jeans and slacks, and none at all with deck shoes or sandals.