If you wear some thin merino wool base layers and also pack a lightweight waterproof windbreaker, the wool will keep you cooler and ventilated when it's hot, and it will keep you warmer and dryer under the windbreaker when it's cool or wet. Wool does double duty- it breathes, it regulates your temperature nicely, it's light to pack, drys quickly, and it doesn't stink after one sweaty wearing like polyester does.
SmartWool and Ibex are two good brands of lightweight merino apparel.
A thin merino base layer under a lightweight water resistant windbreaker will be more versatile than lugging a heavy sweaty jacket around on your bike.
Also, you might want to consider a very bright 'screaming' yellow windbreaker so cars can see you better. Bright yellow windbreakers are common among biking apparel companies.