There are a handful (and only a handful) of blessings that deacons cannot give. There are also very few that priests can’t give, either; but are reserved to bishops.
All the things that are used in regular, daily, parish life can be blessed by a deacon (list not exhaustive):
Holy water
Rosaries and chaplets
Scapulars (conferral of / investiture in)
Ashes
Throats
Animals
Homes
Medals
Crosses, home statues, devotional pictures, etc.
Food and drink (devotional use, and in honor of particular feasts / saints)
Pilgrims
Teachers, students
Sick people
Catechumens
Catechists
Missionaries
Methods of Transport (cars, boats, trains, planes, etc.)
Fields and seeds
Tools for work (hand, mechanical, electronic)
Birthdays
Anniversaries (especially Silver, Gold, etc.)
Parents
Adopted Children
Mothers before childbirth
Mothers after childbirth
Parents after a miscarriage
Elderly people (in personal homes, rest homes, convalescence homes)
Boats, fishing gear
Civil leaders
Meetings
While in the seminary I learned that various Catholic cultures use Holy Water in many varied ways. Some Latinos use it for drinking and cooking, particularly to prepare certain dishes. Others just want a tiny bit to put in a small font inside their home. I have one lady who brings in several gallon jugs to get the water blessed.
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