Can't decide between two Puppies? Take them both.
The F2StickPup tool was designed for multiple Puppy distributions. It puts two partitions on your USB stick. The first is a FAT32 boot and the second, larger, partition is f2fs for the distributions.
There may not be a tool to add another Puppy to a USB stick (yet). I started with two F2StickPup installations, Vanilladpup 10 (sdb1 and sdb2) and F96_CE (sdc1 and sdc2). Note that F96_CE also uses the fossapup64 name. Boot with the Vanilladpup 10 stick and plug-in the F96_CE stick after Vanilla 10 is running. Then:
1. Copy the sdc2/pups/F96 folder to the sdb2/pups/ folder that already has the vanilladpup folder. This takes a bit of time.
2. Copy the F96 menu section of grub.cfg from sdc1 (Mine began - menuentry "Puppy fossapup64 9.6" {... ) and place it below the vanilladpup menu entry section of the grub.cfg on sdb1.
3. Change the stick uuid (like a1eb876a-223d-4683-93df-2800fdcb2da0) in the fossapup64 menuentry to the new stick uuid shown in the vanilladpup menuentry.
4. Change the pdrv= (like lin803125ea) entry in the fossapup64 menuentry to match the pdrv= line in the vanilladpup menuentry section.
5. Look in the sdb2/pups/F96/ folder for a SAVESPEC file. In that file change the SS_ID='lin803125ea' to the new stick pdrv id just like step 4. This file may not exist if no save file was created for F96.
Not too hard. You've added a new Puppy distribution to the original USB stick. Added a menuentry line in grub.cfg for the new distribution and changed the USB stick id numbers for the copied distribution to match the current USB stick.