ELCA Lutheran here.
When I started assisting with communion, it was explained in the training that we were pouring out the wine on the ground as Christ’s blood was spilled on the ground of Calvary. And we, like dropzone, also have a dead spot in the lawn back of our church where we always pour it. We also pour out the water from the first rinsing of the chalice there, and break up the left over loaf and toss it to the birds. Wafers we save and use again.
This is not official Lutheran theology, AFAIK. Our current church is much more High Church than the one I grew up in.
I believe the official teaching is that Christ is present “in, with and under” the bread and wine. This is only in the context of the service of the Eucharist - it would be OK to dispose of leftover bread and wine in any respectful manner. Including eat it with peanut butter, which I once did at my home church.
ELCA will commune any baptized and believing Christian. And we can receive the Eucharist from or pray with anyone we want. My priest brother-in-law will not commune me. Other Roman Catholic priests will. The last time I was out of town I could only find a Roman Catholic church within walking distance of my hotel, so I went to anticipatory mass on Saturday night. The priest there said he would commune me if I went up, and I did and he did.
Regards,
Shodan