I believe that Jesus used unleavened bread, and wine during the last supper. I believe each has a symbolic meaning. The wine, or fruit of the vine, represents his blood, and ties in with so many scriptures that portray Jesus as the vine, with us as the branches. This is a key principle, or description of how we are all tied together, and to God.
I don't think we should substitute anything else for those emblems... although I'm sure there are countless types of unleavened bread that could be used, just as there are many variations of the fruit of the vine that could be used.
As to the notion of people dying because of taking "unworthily"... what does that word mean to you? Over time, I have read and re-read that passage, and in context, it appears that taking communion without "discerning the body" is in reference to how the church at Corinth was partaking in their love feasts. They were not waiting on everyone to be there before starting, and they were over-indulging in the wine, to the point of getting drunk. But, reading the scripture, I believe the BIG issue was, not having all the "body" present when partaking... they were not discerning the body of Christ... the CHURCH.... and in this way, they were partaking unworthily. We are to examine ourselves, as members of the body, and partake as a body in remembering Christ.