Yup, all those things. Go in there and spend some time with our Lord in the Blessed Tabernacle. If you’re driving by and have time, just step in, take a knee in his presence and bless His Holy Name. If you’re planning on doing some bible study, bring it in there and read in His presence. Just go “hang” with Him.
Some parishes will give an access code to verified parishoners if the doors are usually locked.
As far as the Priest being there, you might find them praying the divine office in there throughout the day, but often they aren’t even in their office. There are so few Priests these days that each Priest has to sort of be superman and is running around the city conducting Priestly duties that, in the past, were spread out among many Priests.