As far as I know;
I think cinnamon toast would be "safe". The only annoying part being that they are filled with sugar which I personally try to minimize. Also, they contain gluten.
By choice, my favourite cereals are generally gluten free and not too sweet in general (I have a weakness when it comes to the Sunrise Crunchy Vanilla one's [That I would not recommend when flaring because it's quite fibrous]. Other than that, Golden rice Crispies and Chex.
In general, I had no issue with "kids" cereals: fruit loops, corn pop, alpha-bits, golden graham, frosted flakes etc.... But, these are not the best because they are sugary...
Special-K, Rice Krispies, corn flakes, Cherrios were all fine with me.
The "good" cereals are generally unsafe when flaring; ie: musli, whole-grain type cereals (all bran), wheat-a-bix, mini-wheat etc.