One of the good things about testing myself daily is that I can see the effect of different foods on my sugar the next day. In fact, for that reason, I'd recommend testing to anybody, even somebody healthy.
Of course, if you're healthy, you're less likely to see the magnitude of the changes that I see, just because your body will nullify most carbs naturally.
It is from these observations that I can see that a packet of sweets, say, has much less effect on my sugar than a portion of potatoes. As I've said before, it's not "sweet", but "carb". Of course, sugar is itself a carb, so I'd assume that I would notice it, if I consumed enough. But knowing that kind of information is really useful to me. We're individuals so individual foods will affect us differently, but as a rule of thumb...
The reason I bring this up is because, on two occasions, my sugar has been high this week. Not high, high, but above average. I haven't eaten anything that I'm aware is bad for me, so I've been puzzling a bit over the things I have eaten.
The only thing I can think of, which I ate the day before each reading, was a bowl of muesli. Cereals in general are deadly for containing lots of sugar, but this was specifically a "no-added-sugar-or-salt" variety. So the only sweet stuff should have been the fruit itself, although, granted, raisins are quite sweet. These appeared to be mixed in with oat flakes. Oats are generally my cereal of choice, although heaven knows what other things were mixed in (unfortunately the packet, listing ingredients, is long gone).
So I'm kind-of wary about eating any more of this stuff.
The other thing I observe is that following a "high", it takes my body 48 hours to get back to normal. The next day is always high too, although not as high. I suppose that's just how long it takes your body to eat, process, and get rid of, any food traces. Aside from this being me, that I have to be careful what food I consume, this information is quite interesting I think.