The basic uniform rule is that a team’s uniforms must match and be worn as originally designed by the manufacturer. In CC, a team is 5 or more individuals competing in a race. In Track, a team corresponds with the people on a relay team. Some more specific rules are given below. Understand that if you break a uniform rule and get caught, then you could be disqualified (regardless of how lame you think the rule may be).
Head: depending on weather conditions, toboggans, stocking caps/wrap are permitted. Headbands and other items designed to hold one’s hair (e.g. hair bands) are permitted, if they are not hard (i.e. soft) and if they are fastened or worn securely. No ornamental head/hair items should be worn (as this can be interpreted as "unnecessary adornment"), no hats, and no pre-wrap bands. Headbands cannot include any writing other than the school’s name, and officials are increasingly keen on allowing just one solid color with any head gear.
Tops/Bottoms: uniform singlets and shorts must be worn as they were originally designed to be worn. You cannot roll up your shorts, or tie up the shoulder straps of the top, or anything else. The meet officials at most races will probably also expect you to tuck your uniform top into your shorts.
If you wear a shirt or longer shorts under your uniform, then there cannot be any writing on those undergarments except for a small manufacturer’s logo (if there is one). The under-shirt/shorts must be of one solid color, which must match the color of anyone else wearing a shirt/shorts beneath their uniform. For example, suppose you wear a solid white t-shirt under your uniform. If so, then no one else on the "team" can wear anything under their uniform top other than a solid white shirt - because the team must match.
Hands: gloves or socks may be worn on the hands in cold weather.
Feet: no restrictions on socks, in terms of color or design, but you gotta wear shoes.
Jewelry: no jewelry of any kind is allowed (e.g. earrings, bones through your nose, etc.). Watches are included in this category as well. If you wear jewelry or a watch to a race, then you need to remove those items before reporting to the starting line. Religious medals and medical alert medals are allowed, but these items must be taped to your body (med-alert medals should be taped so that someone can still read what the medal says).
Body markings: no face painting, no temporary markings, etc. If you’ve got what you think is a really cool (visible) permanent tattoo, and the meet referee finds it objectionable, then you’ll be asked to cover that "really cool tattoo" up with tape.