If someone takes an expensive cup of coffee but pays for a cheaper cup of coffee, must he repay the difference? What if he didn't realize it was more expensive? How much must he pay if he doesn't know exactly how much he owes? Sources can be found here. 

Should one say in the הנני מוכן ןמזומן the words במצות עשה כמו שכתוב בתורה?

Why do we daven maariv before sefiras haomer? Are there circumstances when sefiras haomer would come first?

Sources can be found here. 

When erev Pesach falls on Shabbos, which day should one fast? Sources cn be found here. 

Is it permitted to enter a church or a church building to attend an AA meeting? Sources can be found here.