As a avid biker that lives in the land of bikers (Netherlands). Two weeks ago a group of six of us biked around the Bodensee. Here is my advice on individual items that some people overlook:
Gloves - buy the ones that have fingers cut out for this time of year, get good padded ones and make sure the velcro is on the top not bottom, if its on the bottom you will constantly catch them on something and they will come apart. Also make sure they have the largest sweat wipe area around the thumb you can find.
Bibs - Pearl Izumi is top quality here, they actually offer one with a fly in front as well so you don't have to remove half your clothing when you take a piss. Don't waste your time with shorts as the elastic that holds them up will undoubtably pinch somewhere....Bibs won't.
Shorts - see Bibs paragraph above
Shirt - Lots of good brands but make sure it has proper vents and for me at least one zippered pocket in the back for your phone/ID. You don't want to be constantly reaching back there making sure its still there.
Sweat/Dew rag - recommend this to absorb sweat and the little flap in the back will keep the sun from beating down on your neck.
Shoes - I get specialized but whatever brand you get always get a minimum one size up. Make sure they are easily adjustable WHILE you are riding as my feet get hot spots where something is too tight.
Saddle - look at Brooks as they make a great endurance saddle, but whatever saddle you go with get it professionally fitted and adjusted at a real bike store (not REI) as this is probably the most critical piece of equipment on your bike. If your feet go numb during a ride, its your saddle, if you sweat too much and chaff on your gluts again its your saddle.....
Bike fitting - like the saddle do this professionally.
Water bottle cages - two
Under Saddle Bag Small as possible yet big enough to carry one tube, multi-tool, tire changing wedges, patch kit, and most important small first aid kit that has sanitary/anti-infection wet wipes and med-large bandaids as this will fix the majority of scrapes you might get from a fall.
ID Bracelet -
DO NOT LEAVE HOME WITHOUT IT! I recommend road ID, they have both a etched and a full digital model. The digital model has minimal information like name/nationality/age/blood type and then a code on the back with a website address that gives access to emergency contact, allergies, home address, as much info you want to give or not want to give to emergency responders. I prefer this one because you can change your info when you move or a POC changes their phone number.
I also like other items like sleeves (for cold in morning and/or at elevation and hotter in afternoon) that you can peel off and interchangeable lenses on my sunglasses (for varying WX or lighting conditions).
There is a lot more I can type but this will give you a good start. This is obviously for hot weather as its a whole different ball game for cold weather biking. Ask me about those recommendations in the fall.
Best of luck!!!