Just use a larger Zip Lock bag inside and use the tank bag you like. I use that Wolfman Enduro bag on my SE for exactly what you said, wallet, camera, sunglasses, keys and a tire pressure gauge. It has seen hard rain, but not for extended periods of time. No issue.
2007 KTM 525 EXC
2013 Berg TE300
2006 Husky SM610+71 BSA 250 Trials
2011 Beta 300 2T Lim Ed+ 74 RL250 Suzi