You can create filter on model "Product"

On debug mode Settings > Technical > User-defined Filters

Name - As you provide
Model "Product"

Domain - Stock Quant > Location '=' your location (e.g WH/Stock/Truck 1)

[['stock_quant_ids.location_id', '=', 'WH/Stock/Truck 1']]

Available for Users - If left blank is available for all

Default Filter - If you wish to enable else the filter would be available in Favorites

On clicking the Product ribbon on Task, only products in that location would be visible (if set as default).

Here is a way to solve it using Studio. 

Assuming your technicians use trucks / vans where the product come during Field Service jobs. You can add a field on the product, for instance a boolean (checkmark) and name it Truck 1, Truck 2 etc. The field indicates you keep this product in your trucks. It is just for reference, no logic behind it. 

Add the field to the Search view > group by AND create a Filter "Truck 1 = set/true". Now you can use this filter in Field Service products view and perhaps set is as a default filter on the user. 

Here is a video https://youtu.be/Oha35HrpkbM to explain the steps.

Hope it helps.