If you have your heart set on a guide most will supply you with fly gear. If you got into a snook, permit or decent sized baby tarpon I would imagine your 5 weight would leave you under gunned. Your 5 weight however would be quite fun fishing in and around the resorts. I brought a 6 weight for this and had a lot of fun with the reef fish. Bare in mind I have heard of some people being harassed by resort staff and there may be areas that you aren't aloud to fish but I had zero issues in Puerto Morelos. Crazy Charlie's and 3" olive/white bait fish patterns were the best patterns for me. Really neat to have pelicans dive bombing around you and sting rays swimming by your feet while you are fishing in an amazing setting. I had a fly fishing trip booked up North in Isla Blanca but wound up ill the day of and had to cancel. Bottom line is bring your gear, no big deal if you can't use it but you'll regret if you can and didn't bring it.