Great topic. I can't even remember if I've chimed in on this one in the past
Here's my contribution, because I was exploring this very topic personally, to ensure i had covered "all the items" required in a gentleman's wardrobe (my list was about 15 or 20 necessary items). So, I won't be purchasing ANY sartorial items for a good long time.
1. The perfect navy suit. Single breasted, good midweight cloth, 2 or three button jacket and double vented back, flat front trousers optional. The ideal suit for a hot date in NYC, wear the jacket as a blazer, interviews, weddings, or speak at a podium or on TV. Must be altered by a great tailor, not matter where you purchase it-- online or otherwise. 1/4" to 1/2" of shirtsleeve showing at the cuff.
2. A proper white dress shirt, with very little to no tie space where the sides of the collar meet at the top, forming an inverted "V". Trust me-- no tie space just looks sharper. point collar, no buttondowns for this one!
3. An English umbrella. I finally found one that fit the bill at Swaine Adney Brigg in London, solid wood shaft a must. Keep it in the back seat or trunk of the car. #3 can also be substitued for a nice light blue dress shirt. same important points as #2.
4. English plain captoe shoes (or the simplest wingtip pattern you can find) , in black or brown, with as much hand-craftsmanship as you can afford. Crockett and Jones Audley model (which CAN be found at discount, i.e. plal, ebay, etc.) seems to be a great choice, because it has a more elegant shape and overall sharper look than most allen edmonds, alden, or church's I've seen.
5. A good wristwatch, in steel if that's what fits your budget, white or pink gold if your budget allows. Must be the real mcoy-- an authentic swiss army or timex watch beats a fake rolex any day of the week. A steel bracelet goes with everything except a tuxedo, leather band should usually match your belt and shoes.
I would say the gentleman with these five items would be ready for just about anything-- and his monthly budget could surely afford a necktie, white pocket hankerchief (folded in the square TV fold, of course!), or reasonably priced leather belt from time to time-- and these other accessories need not be outrageously expensive or of the highest quality, if you've got the above 5 done right.