During Desert Storm, there was an "Any Service Member" program in which people could send letters and care packages to "Any Service Member".
For those interested in doing something like this, check out the website above. This is actually being discouraged for this campaign. For those who want to do something like this, it is recommended that you make a donation to the Red Cross instead.
Check with your local Red Cross to see if they are only taking monetary donations, or if they are accepting physical goods (Girl Scout Cookies seem to be the local favorite donation). If they are accepting physical goods, one of the high request items is Baby Wipes. Again, though, check with your local chapter to see what is being, and will be accepted.