As far as the beer goes, I think it depends on what is "done" in your circle. If the norm is for everyone to just drink what they brought then Bob was correct. However, if the expectation is bring the beverage of your choice to share, then Paul was correct. I suggest having some clearer rules for in the future. I have a girls group that gets together once a year for a wine party. Everyone brings 1 bottle of wine and we all share. That way we can sample different kinds and see what tastes good. Of course after the first few tastes, its all good, but that's because we are imbibing and not really doing a true wine tasting.
For the unopened food, I can see offering it to the host, but I don't think its required. To me, it doesn't matter what form the contribution is in. If you expect for the contributor to take home their crock pot with the remains of the queso still in it, then they should be similarly expected to take home the unopened pie. Afterall, if the contributor spends $20 on their contribution it shouldn't matter what the contribution is. If the homemade option gets sent home with the creator, then the $20 pastry should too. Either way the contributor gets to take home their leftovers. It doesn't matter if the homemade pie or the store bought pie wasn't cut. If the left overs go home with the contributor, then they go home with the contributor -- cut or not, unopened or not. It wasn't rude, but it still would have been nice for any of the contributors to offer you some of the leftovers.