It depends what time i exercise. Before i was pregnant i used to run at 6am, and then no, i didn't eat, just drank a half pint of water. If i exercise after i would normally eat breakfast (7.30-8am) i just have breakfast as normal.
For a walk i wouldn't normally eat anything special. In fact i only really thought about eating before exercise if i was going to be running more than 4miles or exercising at a similar intensity to running for 45mins+.
You might find it good to experiment. For me being well fuelled for the 24hours BEFORE a workout made more difference than anything i ate or did in the few hours before it, and i found that eating within an hour of finishing up my workout was a lot more useful in terms of how well my training "worked" and how good i felt next time out. Experiment a little, keep a diary of what you eat, where you walk, how far it was what the weather was like and how you felt before during and after, it can be fun and is a great way to see progress and keep motivated.