I have tried other Swiss Army style key holders / key rings on Thingiverse, and found that they all suffered from the same problem: it was difficult for me to actually get at the keys, and near impossible to do it with one hand.
My solution was to design one that folded in the middle to allow for easy access to the keys. Fold it one way to expose one set of keys, fold it the other way to expose the other set. You can even do it one-handed, which you will appreciate if the other hand is holding groceries.
The key holder consists of four identical parts. Print them with no support and a good amount of infill. Please see the side-view photo for the proper orientation. Use 3mm screws and nuts to hold it all together – button heads preferably. You may have to trim or grind the excess length of the screws after assembly. Make sure to pad out one side with washers if you have a different number of keys from one side to the next.