AUTOPICKUP_EXCEPTION is a configuration option that allows you to define what items are automatically picked up, with more precision than with pickup_types. You also need to have autopickup on and pickup_types match the AUTOPICKUP_EXCEPTION -lines.
In NetHack 3.4.3 autopickup exceptions are not compiled in by default, and they're marked as experimental, so most builds probably won't have them.
You can either define the exceptions in the options screen or in your configuration file by putting the following lines in it:
AUTOPICKUP_EXCEPTION=">*chest*"
This will make the hero always drop all items that match the string "*chest*"
AUTOPICKUP_EXCEPTION="<*dagger"
This will make the hero always pickup all items that match the string "*dagger"
If the first character inside the quoted string is greater-than sign (>), then the matched items will be dropped, if it's less-than sign (<), the items will be picked up. Rest of the string defines what items will match for that rule. The string matching allows for basic wildcards, where asterisk (*) matches any number of characters and question mark (?) matches any one character.