I always refused to wear those eyeglass straps. Last summer I was at Cedar Point and again refused to buy them. I would hold my glasses in my hands. Then we went on Top Thrill Dragster. Well..there was no way I was holding them in my hands...my hands would be too busy gripping the bars!!!
The first time I tucked them securely in my bra. It was fine. I WAS worried the bars would somehow crush them though - I can see how it could happen easily.
The 2nd trip I did Dragster again and did the same thing, tucked them in my bra. For whatever reason, this time, they flew out during the ride. I spent the day at Cedar Point pretty much blind LOL! My vision is pretty bad (-5.0) so I can make out colors and shapes. I had to tell my group to be really careful to stay near me so I could keep them in sight. If they went off too far ahead, I had a hard time finding them again. And when we ate at the buffet, it was a riot! I had to get my DD to escort me up and tell me what each dish was as I couldn't see the food without getting too up close and personal!
I recovered my glasses in another trip several weeks later. They have them tagged by date and recover about 30 pairs of glasses a day.
Moral of the story? The straps really do work. They were $1.99 at Cedar Point. I bought them and they're a great souvenir. We've used them multiple times since and they were well worth it.
Also, those small crossbody bags are nice. It all depends what park your DD is going to. I recommend checking to see if there are any rides that DON'T allow bags on. Like PPs have mentioned Cedar Point has several rides like that (with no spot to put your bags) and so does Universal Studios. I bring a very small crossbody bag and for those rides, I would wear the bag under my shirt. It worked well, and I never had any problems being allowed to do so. If I had cargo shorts or something like that, it would be a better alternative. But most of my clothes don't have pockets.