This is the tactical part. This keeps in mind your company could grow fast. This is the difference between working for you or working for a company (well, thats what i think).
----> Inventory Management
Get a reserved, locked space for your IT inventory. (3 keys redundancy, it may be a room, locker, ..?) Try to split it in locations(boxes, shelves, use anything to split the space).
Create a naming convention for your hardware and locations.
Get a labeller (like a P-Touch) and label following the convention.
Keep an inventory. The accountant may already have a software that could help you keeps track of it and this has the plus-value that it will help him/her do the depreciation of the inventory. Avoid notepad or you'll pay for it one day. Excel/Free Office Calc with data integrity rules may be palatable as it may be imported in a future inventory application easily. Lansweeper is a nice freeware for this (requires MS SQL Server).
UPDATE YOUR INVENTORY. When moving stuff, when getting new stuff, etc. or educate the users in doing so.
----> Interoffice messaging, remote access, etc.
Don't, never, forget, the backups. And test your backups. Ok this point is made. Depending on your current IT infrastructure LogMeIn may not be the best solution. Is there firewalls, proxies, etc. if not, you'll need this don't trust the users.
A more professionnal approach would be to set up a secure VPN to your administrative server(s) and/or intranet for remote computing.
For the interoffice messaging, anything goes, you should only look for something that you can have control of. What was suggested by Ryan M. looks like it. If someone gets fired, its not fun if he can speak to customer as he is at the company.
Elaborate a new employee checklist of what you need to do and ask the HR or anyone who hire to send you an email before a new employee arrives. It's not fun to know the exact day the employee arrives and you have an application crashed and waiting for an order to arrive to have to create username and password etc. for that new arrival. And then, when printing the paper for the new guy, the printer jams.
Learn to use an agenda or a PDA or Outlook or anything like this. There are some frameworks for the use of those like 'Getting thing Done'. You'll get requests from the entire planet and sometime even from other planets. Schedule tasks like 'taking the inventory' and 'testing backups'.
Write documentation on what you do technically when you do it. And develop a filing system for knowledge.
Draw diagrams of business process. You could use the BPMN framework for example. So everybody knows how things are done, the workflow and its easy to train new people.
Ask for email requests Don't accept to do things when asked on the fly while you are doing something else.
Prepare forms for the most common requests You'll ensure you get all the information you need the first time and will not lose time asking for the details you need. You could refer to 'the most common requests' as 'Service requests'. I know its bureaucratic but you may add a unique number to those, so you can quickly refer to 'i'll need the form Win-102 for this'.
Get a vulcan they have no emotions and good memory.
Following all those principles should avoid you a lot of sh.t hitting the fan. Show this to your boss and ask for a raise. Two raise, since you're doing 3 jobs.