Loft insulation and part bag of plaster (Boulton DE24)

Hello

We've had a new loft hatch fitted and now we need to make good around the new hatch, and re insulate some sections.
We have most of bits to do the job but would like to avoid buying a whole bag of plaster for a patch up and insulation when we probably won't need full pack of either
Can collect after 4pm evenings / weekends or potentially to work or on lunch break.
Thanks