Create a library (File > New > Library). You'll be asked to save it to a location.
Create your slug as a text frame in an InDesign document. Either drag it to the library, or click the New Library Item button.
When you need a slug in a new document, drag it into your document.
You can also create a Document Preset which sets up the page size you want to save, as well as setting your slug or bleed areas. Use the preset to create your new document.
Either save the Document Preset from the New Document window, or by choosing File > Document Presets > Define.
You might also want to consider making a template file rather than dragging the slug info from a library. You can put it on a master page...