Improvised Weapons - I actually studied this once. Pretty cool concept actually.
Assuming you aren't carrying your pistol or packing a pocket knife?
A handful of change, or your keys, will add some impact to a thrown punch.
I suppose the obvious broken glass bottle, but these days that would basically say beer bottle ( or a nice bottle of Thomas Kemper ).
Old school car antennas come off in a "snap" ( pun - zing ) and make a great improvised short range whip.
The "mail pickup" red flag off a mailbox should come off fairly well, and could be used to some effect. Still puts you "in range" of counter strike.
Any type of construction site, fairly common the last few years in most areas of the country, would lead you to rebar, 2x4's and lots of other "club" like weapons.
Trash cans are a good source of improvised weapons:
The lid off a soup can.
An Aluminum can, crinkled and twisted open, leaves a nice, sharp edge.
The plastic "clamshell" off a million packages sold in this day and age will lay an opponent open quite quickly if you care to close the distance.
Putting your cellphone, assuming you can't use it for it's intended purpose, and/or your keys into a pocket in your jacket can allow you a weighted, almost morningstar type of flail, to swing by the sleeves with effect to keep an attacker at bay.
Decorative rocks or bricks from a persons' front yard or garden. Used as a crude brass knuckle or club.
A small diameter branch, or limb off a sampling, can be easily torn off and used as a make shift riding crop or bullwhip if you run your hands up the shaft and remove most of the leaves to allow less aerodynamic resistance.
That's just off the top of my head from the classes, I will need to give it some thought and see what else I remember...