Lighter Shirts
With shirts, fabric makes a massive difference. For summer, I recommend shirts that are made from either light cotton, linen, or a blend of the two. I generally go for cotton since linens tend to wrinkle, but if you own a steamer and do not mind wrinkles, linen and blends can offer a lot of airflow.
For a specific cut, look into the Guyabara: it’s a shirt made popular in Cuba by the Spanish, which has pockets (for cigars and sunglasses) as well as a generous cut that helps air flow through the shirt to keep you cool. They’ve become my summer go-to in Miami.
If you usually like slim-fit shirts, it’s also a good idea to think about a little looser fit for the summer. Minimizing the contact between the shirt and your skin is a great way to increase airflow, and give the sweat somewhere to evaporate other than directly into your shirt. Shorter sleeves are a good idea, too, though I typically go with long sleeves to keep the chance of sunburn down to a bare minimum. Sweat is slightly annoying, but skin cancer is a much more serious problem.
Gold Accessories
Typically, I prefer to keep my accessories, whether it’s sunglasses, watches, belts, or pocket knives relatively understated, when it’s bright and sunny you can get away with a fair bit more.
When you’re already doing a relatively casual outfit, then it makes sense that you can also use accessories that are more casual and, in this case, evoke ideas of things being bright and sunny.
Of course, actual gold watches and the like can be outrageously expensive, especially for items that you don’t wear terribly often. To this end, I want to make a specific recommendation. If you’re into automatic watches and want one that you can afford, the Seiko 5 is hard to beat. I have three currently: a stainless steel banded model, a gold one, and a third one that has a blue face that currently sports a blue and white striped dial. On sale, each of them was under $200 and I get compliments on them all the time.
In a similar vein, a pocket knife with brass bolsters is a tool that not only stands out but will age nicely with time. For summers, it’s not a bad idea to get a model that also has a bottle opener attached. A corkscrew might not be a bad idea either if you can find a model that suits your aesthetics.