Great question Tina! And great advice Juan!
Juan is right…it’s not so much fun starting with everything wet. However, in the end, it’s just water and it’s summer. So it’s not the worst time of the year to get damp. That said, if you do want to cover your bike, you will need to check with the race director. Many races banned plastic bags because once they were used, then they floated around the transition area and elsewhere as rubbish. It’s wasteful and potentially harmful and hazardous. So many races banned them.
Instead, what I would recommend is that you don’t leave anything additional overnight besides your bike. And in the morning, do your best to keep things dry so you can start with them dry. More importantly is how you handle rain on the bike. I would recommend that you just dial back your pace by a notch. Be very careful of others and their bike handling skills in wet or slick weather. Limit your time in aero if it’s raining because you have less ability to steer and react in this position. Also, put slightly less air in your tires so that your bike tires have more traction on the road.
Hopefully the weather will hold for you. But if not, at least you have some good ideas how to best manage the non ideal weather. Embrace it as it’s all part of the experience!
Good luck at Poconos!