The first thing to keep in mind while packing, is that Cariocas dress casual and light. The second is that if you forget anything, you will find something similar at local stores for a bargain. Now let's see what makes sense and what doesn't.
Bring your favorite pair of sneakers. You will be walking around a lot, and you need very comfortable walking shoes. Another pair of casual shoes for the evening will do. You will need dress shoes only if you are coming on business, or planning to go to the more sophisticated nightclubs. Forget your beach sandals at home, and buy a pair of Havaianas flip-flops at local shops.
Comfortable clothes are a question of survival, especially in the summer. Choose natural fabrics that breathe, like cotton. Bermudas or cargo shorts with lots of pockets are great for the day. In addition to a pair of jeans, bring chinos or khakis for the evening.
You don't need anyone to tell you that you will need plenty of T-shirts. Bring something dressier for the evening. That little black dress works everywhere, and for the boys a button-down shirt without a tie should be enough. Remember again you may sweat, so pack something suitable (some colors are better than others).
Bring a nice sweater if you are coming during the colder months. Bring a sweat suit even if you are coming in the summer - you may want to sleep in it when you turn the air-conditioner full blast at night. A favorite casual jacket is a good addition, if you are coming in the winter or fall. A light rain jacket is always a good idea, as it does rain in Rio. A suit and tie are not really necessary, unless you are coming on business.
Be prepared for hot and sunny days even in the winter. Pack your favorite bathing suit or bikini to wear on the first day. As soon as you get a chance treat yourself with a visit to a bikini boutique. Many guys wear Speedos under their surfer's trunks, and take them off every now and then to keep the tan line in check. Carioca men favor wider swimming briefs, and bikini briefs and thongs are not considered sexy even among gay men (see beach etiquette).
Now a special note to socks: Keep your knee-length white socks back home, they are a fashion no-no in Rio. If you want to look like you belong, go for shorter socks, and do not pull them all the way up. Last but not least, black umbrellas at the beach make you look funny - especially when you're fully clothed.
Gadgets, Accessories, etc...110 V and 60 Hz is how electricity goes here. A few hotels have dual voltage in the bathroom. Make sure your electric razor, toothbrush, and hair-drier are suitable to our standards, or they will only take up precious space in your luggage. If you're coming from Europe, in addition to dual voltage you may also need an adapter plug. The sockets will take plugs with round or flat pins, but not the flat ones where one side is wider than the other. Computer outlets are standard around the world, and Internet access from your room is possible to find at better hotels.You already know that you are not supposed to bring your precious tiaras and family jewels with you. Sometimes it is very hard to tell a fake from the real thing, thus avoid flashy yet realistic-looking stuff. There are digital clocks all around town, so watches are also optional. If you like to keep track of time, bring something replaceable (waterproof is a plus). The best advice for you not to become a victim is not to look like one.Women who cannot live without a heavy layer of make-up may experience their faces melting in the summer heat. Wear as little make-up as you can live with, and make sure it is suitable for hot weather. Invest on top quality sunscreen, and let your skin breathe freely. Brazilian women generally wear very little eye-shadow, and also go easy on mascara. Nobody wears make-up at the beach. Bring a high SPF sunblock lipstick instead.
Quality shampoos, grooming, and beauty products are easily available at import stores and better supermarkets. You will find major brands like Revlon, Pantene, Finesse, Klorane, Neutrogena, etc. If you are very fussy or extremely allergic, though, please bring a little of everything you feel you may need! The same holds true for chewing gum, candies, and all those essential unessentials we tend to become attached to. And if you have smoked the same cigarettes since the beginning of times, bring a carton from home. You may find Brazilian cigarettes too strong for you. Plus, the graphic images they show on the back of the packs are enough to make you quit for good.