Just make a protocol up then.
If its only going to be used for your own devices, and not interfaced to anything else with a specific protocol, then just make one up.
form a string that you print to the serial port, seperate each variable in the string with a comma or something. This is what I am currently doing for one of my projects.
I have a start character so the PC can easily fix onto the start of the string. My start character is the STX character which is HEX 0x02.
I then have the data I want, seperated with commas. ie DATA1,DATA2,DATA3
I then have two end characters to show its the end of the string, which are Carriage Return and Line Feed. 0x0D and 0x0A in hex.
Start and End characters make it very easy for the PC to lock onto each 'frame', so it gets the entire frame and not the end of one and the start of the next and try to perform some sort of calaculation on the data.
So basically I send a string like this:
Hope that is of some help