Even the geologist use small notebooks like this. You could put little sketches of the place you found some rocks and call your sketch a name and number. This will help you remember, when you get home, just where you found that pretty one. This book is known as a field book and you can keep it with your mineral collection and field trip tools. Another important and inexpensive item you really need, is wrapping paper for your specimens.
Old newspapers do just fine for the larger pieces.
For very small pieces, I like to carry some empty film containers - the little round plastic boxes with a tight lid. You can put a little toilet tissue in these containers to cushion your find. When you get more experience with rock hounding, you may want to get a rock hammer and a couple of cold chisels. Some good spots for looking for specimens for your collection are along beaches among the rocks, in gravel where you find it - even your own driveway, sometimes. Interesting rocks and minerals can be found almost anywhere.