Baggy clothing will not be suitable for road riding; you go much faster and flapping clothes will drive you bonkers.
A small saddle pack can carry a spare tube, two tyre levers, multi tool, CO2 inflator and a couple of cylinders. Scott make good ones. A bottle cage and a computer so you can check distances and average speeds.
Carry a cheap old topup phone, energy bar, cash and a compact waterproof in your jersey pockets. If you’ve got the cash, the Castelli Sottile jacket is a favourite for good reason; it works and is slightly stretchy meaning it fits snugly and doesn’t flap.
Don’t over-inflate your tyres, modern tyres 23mm or 25mm wide are designed for comfort and a pressure of 90 to 95 lbs suits the average rider. Decathlon’s track pump is excellent value and has a skinny barrel for high pressures.