Good Snacking Ideas and stomach toning

Hi,
I have already lost a stone eating better and doing a little exercise in the house but got to the point I knew I needed to increase my exercise to get to what I was did my Masters(didn't eat well and had little physical activity). Since getting myfitnesspal a couple of days ago, I've had a few shocks about the sugars in my food choices. I think I will now do better with my diet using the app as a guide to what I'm eating. I was wondering if anyone could recommend any low calorie, low sugar snacks that will help me through the day. I tend to get hunger pangs in the afternoon. I should mention I am a coeliac. I was also wondering if anyone could advise me on any good lower abdominal work outs besides crunches as I quite like to vary my workout to keep myself interest. Thank you in advance :)

Kirsty