Brava, my approach is similar to Bryony's.
For rides longer than an hour or so I use a combination of fast acting and slow acting sugar/starch to my keep my Sugars up. I drink Ribena or Hi-Juice and eat things such as Malt Loaf, Banana Bread, Tea Bread, Fruit Cake, Scones, Flapjacks, etc.
Personally, I find a mixture of low and high GI food/drink is a good balance for cycling. So I will consume at least 500ml of drink per hour that contains between 5% and 7% of sugars i.e. an isotonic drink. As well as this I will eat a small handful piece of food after each hour. If I'm on a long ride such as an all day Audax I will also eat a meal and take a very small amount of insulin. If riding a Sportive then I probably wouldn't get the opportunity to stop for a meal with insulin so I will just snack all day.
The effects on your Blood Sugar levels could last up to 24 hours if you've been on a very long ride. You'll have to give us an idea of the type of cycling you do i.e. intensity and duration.