Download ubuntu packages now install all later

I'm looking to use apt-get for Ubuntu and yum for Centos to do the following as root:

1) Ubuntu: apt-get update ; apt-get -d dist-upgrade
to just download the update items for later install

2) How do I install the previously downloaded files at a different time? I was thinking apt-get -f install but can't tell if t will get all the updates. - my 2 Ubuntu systems are both up to date so I can't test this yet

3) yum for CentOS doesn't seem to have a download only option. This part of the question is not as critical.

Thanks in advance