My first post would be this - something that the business man should have in his wardrobe. Everyone has their opinion about this, but this is my point of view.
1. Basic White T-shirt
This is the basic of the basic, something that you could wear with a pair of jeans and chinos, as well as with a suit. However, it has to be fitted and clean. Oversized and stretched out neck doesn't look very appealing.
2. Brown monks
These are great for both dress up or down, would great with suits or denim jeans and chinos. Many people now a days, wear them with invisible socks, but you could certainly wear them with regular socks.
Many people might be interested in Apple Watch now a days, but I personally prefer something like this chronograph watch. It doesn't have to be expensive, something simple. It looks dressy but chronograph actually gives the casual look as well.
Basic V-neck sweater, in either merino wool or cashmere. This could be worn over your skin or over T-shirt. However, make sure to brush it after you have worn it all day to prevent from peeling.
5. Suede Chukka Boots
These are other alternatives for dressing up or down, but probably more so for winter time here in Sydney.
6. Navy Suit
This is a staple outfit that every grown man should have. This is good for friends' weddings, formal occasions, business, interviews, pretty much for every occasion. It will go with any shirts and any ties.
7. White Oxford Shirt
This is also something that will go great with both dressy and casual occasions like business, formal, and just hang out with your buddies at the bar. I might personally recommend you to get [Royal Oxford] over regular [Oxford], which will give you slightly dressier look.
8. Navy Tie
Again, this is something that you don't need to think about how to match with the shirt or the jacket. Plain color makes it easy to match with even patterned shirt. You might want to choose to have some texture in the fabric so that would work with both suit and casual outfit.
10. Cotton Chino Pants
Like denim jeans, these are good alternatives to dress up or down, casual Friday for some business men or every day for tech related men, great for going out. Especially these usually have some stretch in them, and variety of colors.
11. Black Dress Shoes
To be honest with you, I personally don't like black dress shoes, they make such a heavy look. However, like navy suit, these are great for any occasions. Even with denim jeans and buttoned up shirt, it will give you a dressy look.
Since the outfit is becoming more and more casual, these sneakers could be accepted in certain business industries, I sometimes wear them with suits, just because my industry allows as fashion point but not so much for bankers and lawyers. However, they are great for weekends. Plainer and leather might give you slightly more elegant look.
13. Navy Sports Jacket
This is another alternative to the suits, you can wear this jacket with dress pants, denim jeans and chinos. Go out to dinner with your partner or business meetings, throw it on over your T-shirt, it will work great.
15. Trench Coat
This is a nice to have item more than must have, especially in Sydney. If you are in 4 seasons country, it could be a must to have item. This will work with dress up or down look.
16. Denim Jeans
This may not work for a business man, but it's good for maybe a casual Friday and weekends, or if you are in media or tech industries, it might be okay to go to work in. However, oversized and tired looking jeans won't do the job. They need to be fitted and clean. Since it is a warm climate in Sydney, 10oz might be a perfect weight all year around.
17. Polo Shirt
This is another alternative to the white T-shirt, will give you much more dressy look than a plain T-shirt. It is something that you could wear by itself or underneath of the jacket.
This is another item that many people lack to have, like a wallet. In my opinion, every grown man should have a bag. Material and style don't matter, something that you could keep your stuff in, instead of carrying in your hands or in your pockets. Any pockets should be used to carry a minimum thing, not for heavy items so that the shape of the garments won't change.