I'm not a fan of the whole "sad things on index cards" schtick, but that's the territory my games tend to inhabit. I prefer to quickly write something down on the fly, then throw it away when it's no longer relevant...rather than write it on a character sheet, rub it out, write something else, rub that out...etc.
If this mutant animal game is going to be based on FUBAR, then it's definitely going to fall into the "sad things on index cards" genre, but I'm thinking pocketmods for the character books.
Title: character's name, their animal type, a couple of permanent traits that define them, and a picture.
First opening: the core stats that you need for play.
Middle opening: quirky animal powers and likely transformative effects when mutagenic weapons are used on the character (evolution and devolution)
Back opening: character history, and relationships (to people, places and things)
Back page: unsure (maybe a quick rule recap, maybe an equipment list...I don't know yet)
I've also been thinking of a major revision to FUBAR, nothing as dramatic as what I've been doing with Walkabout (which is also a direct descendent of FUBAR), more of a linguistic clarification. This has come from looking at +Jeremy Keller's Tech Noir and from studying linguistics at university at the moment.
I really like the idea of using nouns, adjectives and verbs as procedural elements in play. They add structure to a freeform system that is designed to simulate storytelling rather than the mechanisms and physics of the world.
I'm thinking of renaming all of the FUBAR skills into verbs for this game...then when the GM asks a player what they are doing, the player can respond with a gramatically correct Subject-Verb-Object sentence using the specific traits they are using in the game. "I (the subject) am going to Run (the verb) to the Car (the object)". This means we can apply bonus traits as adverbs to the action ("run quickly"), or add more significance and interest to the subjects and objects through adjectives ("the high-performance, expensive car"). If a character wants to do something to achieve a story goal, they still eliminate tokens from the GMs pool to get closer to the conclusion, but if they want to modify an action or a target object, their successes basically add or subtract adjectives or adverbs.
I think this might make it more logical for new players as well.
I thought anout this last night when I was digging through my hard drive and found a players guide to FUBAR that I had written a couple of years ago. Most of the ideas from that guide have found their way into Walkabout, but there are a few core concepts that have just sat in the shadows waiting for the right time to come out.