Depending on how much of the periodic table you have memorized you could go a little further with decimal notation to give atomic number, atomic weights, and specialized symbols.
H, 1, 1.01
He, 2, 4.00
Li, 3, 6.94
Be, 4, 9.01
B, 5, 10.8
C, 6, 12.01
Past that point you can probably just get away with reference by atomic number and you only have to have the periodic table's order memorized (...boron, carbon, nitrogen, oxygen, fluorine, neon, sodium, magnesium, etc). Then you can diagram basic molecules like water as "(1)-(8)-(1)". Nail down the meaning by spitting for a demonstration of "liquid", and maybe come up with a convention for angles and show the angle between the two hydrogen dangling off the oxygen being ~104.5 degrees. Ask for 80% gaseous "(7)-(7)" and 20% gaseous "(8)-(8)" plus water to explain your biological requirements for a few days. Diagram glucose, fatty acids, salt, and essential amino acids so they can fabricate enough food to last until scurvy or some other nutrient deficiency kicks in.
That should give enough time for them to decompile our genome and learn English if the aliens are any good at being our technological superiors :-)
While waiting for that, constellations might also be a good place to go, if you have access to the night sky or a portal in their ship or something? The apparent movement of stellar objects can serve as a chronometer (if you can still see the sun or the moon or something). Once you've got a stable unit of time and a stable unit of distance you can start talking about stars by pointing and describing light years. If I remember correctly, Vega is around 28 light years away, Betelgeuse is about 600. (Google says... 25 and 646.) Then you can ask "How far have you traveled to get here?"
You should be able to get time just by labeling the orbits in your diagram of the solar system. Of course, you'll have to remember that the sidereal year is one day longer. Just label the Earth's orbit "year" and the Earth's spin "sidereal" and then write 1(year)=366.25 days. Hopefully the aliens are tolerant of approximations. They may first think these are distances, but their next guess when they see the math doesn't work would probably be time.
Then draw a line on your diagram between the Earth and the sun. Thats 1AU. The speed of li...
Allow me to propose a thought experiment. Suppose you, and you alone, were to make first contact with an alien species. Since your survival and the survival of the entire human race may depend on the extraterrestrials recognizing you as a member of a rational species, how would you convey your knowledge of mathematics, logic, and the scientific method to them using only your personal knowledge and whatever tools you might reasonably have on your person on an average day?
When I thought of this question, the two methods that immediately came to mind were the Pythagorean Theorem and prime number sequences. For instance, I could draw a rough right triangle and label one side with three dots, the other with four, and the hypotenuse with five. However, I realized that these are fairly primitive maths. After all, the ancient Greeks knew of them, and yet had no concept of the scientific method. Would these likely be sufficient, and if not what would be? Could you make a rough sketch of the first few atoms on the periodic table or other such universal phenomena so that it would be generally recognizable? Could you convey a proof of rationality in a manner that even aliens who cannot hear human vocalizations, or see in a completely different part of the EM spectrum? Is it even in principle possible to express rationality without a common linguistic grounding?
In other words, what is the most rational thought you could convey without the benefit of common language, culture, psychology, or biology, and how would you do it?
Bonus point: Could you convey Bayes' theorem to said ET?