You can download and save to cd software from the repository.
when you ready to install it you have a couple of option.
1) create a local repository on your hard drive.(Difficulty: medium)
2) use kpackage to install.(Difficulty: low) does not support dependency resolution when installing from a deb file.
3) use synaptic to both download and install the packages.
I use option three. synaptic will let you select the packages you want and generate a download script to download the package you need and its dependencies. So you can store every thing you need to install a particular package in one place.
Synaptic also give you the option of installing the packages stored in a particular folder and will resolve dependencies. Alternately you can have synaptic just download the package without installing them while your online then just install them later.
Ubunutu/Kubuntu online repository: http://packages.ubuntu.com/gutsy/
You can download packages manually from the above address.