score:1
The more information you have, the more chances you have of taking advantage of it. So, obviously, taking all your information with you gives the most benefits but I suppose you are asking because you might also find it cumbersome to take everything with you.
Personally I almost never carry physical cards. Instead I have a lightweight app on my phone to take text notes and one of these notes is simply a list of my reward programs with the numbers. No user name and password are actually needed to collect, only to redeem, which is fairly rare during a trip unless you have not booked in advance. So, I recommend you at least take all the numbers with you.
The best tip I can offer though is to avoid fragmenting your points by only opening one account per alliance unless you travel very frequently. That way your balances will go higher (in fewer accounts) which lets you reach reward levels sooner and reduce chances of points expiring due to inactivity on some accounts (point expire after a certain time on most but not all programs).
Most often if your flights gets cancelled and you get rebooked, the airline will first book you on one of its partner airlines, so the same travel reward program would collect points. Only when partners are not available do they book on an unrelated airline. It does happen but fairly rare in my experience.
Upvote:0
Pretty much any airline and/or hotel chain has an app and an online portal. It's useful to have the user names and passwords with you just in case you need it. You don't need the actual physical card or membership numbers, if you have internet access.
You can decide to download and install the apps as well, which sometime speeds up booking, checking in, getting boarding passess, etc.