It depends on your business model… but start with these basics and tailor from there:
QuickBooks: best accounting software out there.
Zenpayroll: best payroll provider (for up to 100 employees).
Zenefits: to manage benefits and PTO.
Bill.com: to manage your AP
Salesforce: to manage the sales pipeline.
Expensify or Abacus: to manage your expense reports.
DropBox or Box: to manage and share files.
Gmail: to manage your company’s email.
PostMates: to keep the troops fed :)
HitList: to balance your life.