With the idea I was going through, your summons would be stronger depending on the quality / cut of the gemstone you have and the quality of your bag container. /shrugs

I just really love Summoners so I always think of different ways.

Like you said, a Tome would be really cool as it would be held in the character's left hand and the right hand would write magical symbols in the air as magic sprouts from his/her finger tip.