If I go to Confession, and then later on remember something I needed to confess, can I still receive the Eucharist, and then include the sin in the next Confession?
Yes, you can receive communion. If it was a venial sin you have no need to confess it at your next confession. If its a mortal sin then you can confess it at your next reasonable opportunity:
Q. 793. Is our Confession worthy if, without our fault, we forget to confess a mortal sin?
A. If without our fault we forget to confess a mortal sin, our Confession is worthy, and the sin is forgiven; but it must be told in Confession if it again comes to our mind.
**Q. 794. May a person who has forgotten to tell a mortal sin in confession go to Holy Communion before going again to confession?
A. A person who has forgotten to tell a mortal sin in confession may go to communion before again going to confession, because the forgotten sin was forgiven with those confessed, and the confession was good and worthy.