Many homeless are hidden, for example children sleeping on a relative's couch, families in shelters and situations like that.
For someone on the corner one thing to do is keep food in your car that does not need to be prepared like granola bars, tuna in a pouch, canned sausage, cookies. If it's a hot climate keep water bottles or juice boxes. You can buy coffee or meal for a person outside of fast food or a gas station and then give the person the receipt for it. Some things depend on the climate. Up north in big cities buy blankets from the thrift store or emergency wool blend type of blankets to give out. Thrift stores have amazing deals when they close out the season. Look out for large jackets, sweatshirts, wool sweaters and wool scarves.
In the US Most of the homeless in shelters who have children will be able to receive some SNAP (food stamp) benefits. Personal items are always needed as they cannot be bought with food stamps. Feminine products, diapers (especially in larger sizes), dental care items, shampoo, underwear in adult and children sizes, socks, pajamas for children and adults, are always needed. When you pick up this stuff for yourself consider buying 1 more and bring it to a local shelter. Gift certificates for hair cuts and common fast food (McDonalds, pizza) are useful too.
Even if you don't sew, you could organize an "ugly quilt" session at your church on a Saturday. You could talk to local quilt group leaders and pick a date.
-Tiffany