I guess the most optimal way to commute between La Jolla (to be specific, say from La Jolla Village Lodge) and UCSD is bus 30. According to the MTS website, there are 3-day passes available (that option would be perfect for me). However, I believe I need to get a Compass Card to load a 3-day pass on it. The aforementioned web site indicated that there are no locations where I can buy a Compass Card near the hotel I mentioned. What are my options? E.g. can I buy the card at the airport upon arrival? (I'd like to avoid using the MTS app if possible, since it has horrible reviews, and also since I'll need receipts which I'm not sure whether the app provides.)
You will be able to get a Compass Card at the airport, either before or after you claim your baggage.
From the MTS web site:
Ticket Vending Machines for MTS services are located near the Information Centers of both Terminals 1 and 2, as well as at the Middletown and Santa Fe Depot stations. Ticket Vending Machines sell Compass Cards with one day passes, multiple-day passes, and monthly passes. You may also reload your existing Compass Card. The machines accept cash (and give change up to $15) and credit cards.
In Terminal 1 the information center is across from baggage carousel 2. In Terminal 2 the information center is between baggage carousels 3 and 4.
If you exit baggage claim in Terminal 1, the bus stop will be directly ahead of you. If you exit baggage claim in Terminal 2, turn left when coming out the doors to reach the bus stop.