I have an iPad, iPod touch (First edition), and iPhone. I personally keep Apple stock afloat :-) Of all the devices, the iPad is my favorite. I use it in class with the application "Noterize" It allows me to import PDF and powerpoint presentations, then record the lecture, highlight slides, and type or handwrite notes on each slide. Saves me a fortune on toner cartridges, and the audio recording is specific to each slide. So if slides 1-6 are no problem, but slide #7 is kicking your backside, then scroll to slide #7, read your notes as you listen to the lecture specific to that screen. No more scrolling back and forth trying to find the part you are looking for.
Many, many of the textbooks are available online. Again, no carrying the 12 pound textbook. However, before investing in the e-version of your textbook make sure it is not in Flash mode. As you may know Apple does not support Flash on its mobile devices. Kozier & Erb's Nursing fundamantals 8th edition is unfortunately a Flash version. (Costly learning mistake.)
I use Davis Drug guide from unbound medicine ($49.00) approx. the same as the print copy. It includes updates throughout the first year. Subsequent updates will cost another $49.00. But the application will continue to work at the end of the year. However, my experience at the hospitals during clinicals is hospital print editions are usually much older than 1 year. I particularly like the "favorites" ability. As I prep for a client, I look up each drug for my client, and add it to favorites. Then I have all the meds prepped, researched, and available at a seconds notice, if I have a question. At the end of the day, I delete all the favorites (30 seconds max) and I am ready for my next clinical client.
Epocrates available for free, has a great interactions feature for medications. I can again add all the meds for my client, tap Interactions checker, and it gives me a list of possible interactions ranked by severity. Epocrates also has images of the medication as availble from different manufacturers. Perfect for when the client says "That doesn't look like my medication."
I use many other applications for help here and there. But so far, these three are my all time favorites. If you took them away, I would be seriously bummed.