There was bread and wine. When he broke the bread he told them to do this in remembrance of Me. He noted “this cup which is poured out for you is the new covenant in my blood.” He’s talking bout the sacrifice he’s about to make for our sins. The new covenant comes about through His shed blood. He makes this clear in Matthew’s account when He notes,”for this is my blood of the covenant which is pours out for many for forgiveness of sins. He also calls the drink the fruit of the vine. It’s understood from the context the wine is symbolic of His blood.
But he doesn’t say the contents of the cup is symbolic of his blood. He says it IS his blood. And of course, it is the same blood as the blood he was about to shed the following day.
But then you have to ignore John 6, where he says we are to eat his flesh and drink his blood. He says his flesh is “real food” and his blood is “real drink.” There is much more that he says that militates against the position that the sacrament of the Eucharist is merely symbolic.