Documents needed to confirm expenses
In Russia original documents are needed for most expenses to make them tax deductible. Without origianl documents in the correct format according to Russian accounting rules expenses can not be deducted.
While in many countries already pictures or other electronic documents are sufficient in Russia often originals are required.
In general on all documents relating to expenses, an employee must document if the company has paid him or if he has paid himself. If this is not clearly documented, then an accountant must review this on an individual basis. And in practice it is an area where control is needed by management to avoid a company to pay “double”.
This is especially critical for foreign companies in Russia with expats if the expat also has a business card not tied to the local legal entity but from the mother company abroad.
Restaurant Bill
Valid bill from Restaurant. Easier said then received.
Restaurants often hand out pre-bills (just a printed document with the sum to be paid but no legal information like the personal tax reference number (INN) etc. For tax deductibility it must be a full bill which contains details such as the personal tax reference number (INN) and other information. 
To add an expense, documentation for the business purpose and the participants involved is needed as justification.
A self-written bill with stamp is also not sufficient.
If an insufficiently detailed restaurant bill is received, then this amount cannot be deducted from the taxes. If insufficient documented bills are refunded depends on internal rules.
Hotel
If paid by employee – bill page and payment stub from the terminal (kassovyi chek / кассовый чек).
Company paid the bill – Confirmation document about provided services from hotel (akt / акт) and document for VAT offsetting (schet-faktura/ счет-фактура). 
For hotels abroad two documents are also needed. The printed out bill and then some level of confirmation that it was really paid (e.g. a “Paid” stamp, a print out of a private credit card, a print out from cash terminal if it exists etc.)
Often if company has a continuous relationship with a hotel then the accountants have set up processes to exchange the printed, signed and stamped accounting documents when the company pays the hotel. On a trip to various locations in Russia it takes substantial time to receive all these documents by post.
The consequence of not receiving the document is that for tax purposes the expense is not deductible.
If a document is in a foreign language (even in English), then an official translation to Russian is needed to deduct the expense according to official rules. In a tax check none-translated expenses could be excluded from the profit tax calculation. In practice though few companies translate all these documents to Russian.
Airplane travel
The ticket stump from the airline or the printed out electronic ticket is needed.
If personally bought and the ticket is electronic, then the ticket must detail the sum paid.
Train ticket
Same as airplane ticket
Purchase of goods
Documents about the purchase which are the kassovyi chek / кассовый чек or the tovarnyi chek / товарный чек.
If goods cost more than 100, 000 rubles (including VAT) then the goods must be bought officially. Also if goods are not to be put on expenses, but added to the balance sheet, then it is better they are bought officially by the company. Sometimes prices for buying goods as a company are slightly higher than those for buying them as individuals. 
If goods are bought abroad then special rules apply and any purchase, especially large ones, should be discussed with the accountant ahead of time.
Gas
In general being refunded for gas purchases or for private use is a special topic. A high number of documents are needed if the amount is to be expensed.
Tipping in restaurants
Tips are often provided in cash and are not on the bill or on any additional document.
An additional self-written document can serve as a basis for refunding. It cannot be deducted as an expense from the profit tax, though income tax is withheld. The amount can be grossed up.