Saving shopping cart permanently (without login)

[PM Vibes]

Since Zen Cart didn't offer the "buy without login" functionality, I modified some code for my purposes. Customers add items to the shopping cart, then just write a form and we receive their order (no registration/login - no immediate credit card payment). All work fine.

Now customers are asking for saving the shopping cart they made, so they may continue the order on a second time (after some hours, days or weeks).

I know I have to work on sessions and cookies...
I understood more or less how it works (ex. the db sessions table) but I'm not very sure on how can I make this change.
I'd just need a sort of "list of steps" explaining how can I do this (without writing all the code and files changes, etc. I will try to manage for that), so I can focus myself on them without spending too much time on this!

Thank you.

[superprg]

You can change the sessio expiry tme to be indefinite or like 20 hous or something but what if the customers reboots the system?